g/person/day.
This Guidance document represented current agency thinking in regards to the available science at the time it was issued. It no longer represents the current state of science and is presented here for the historical record only.
United States Food and Drug Administration
200 C St., S.W.
Washington, D.C. 20204
August 1993
i. AUTHORS AND CONTRIBUTERS
ii. EXECUTIVE SUMMARY
iii. FORWARD
I. STATUTORY AUTHORITY
II. PUBLIC HEALTH STATEMENT
III. SAMPLING OF AND TRACE ELEMENT ANALYSIS IN SHELLFISH
1. Sampling
1.1 Field Sampling Procedure
1.2 Laboratory Sample Preparation
2. Analytical Methodology
2.1 Mineralization
2.2 Determinative Techniques
3. Quality Assurance/Quality control (QA/QC)
IV. CONSUMPTION AND EXPOSURE ESTIMATE
1. Shellfish Intake
2. Chromium Concentrations in Shellfish
3. Chromium Exposure from Shellfish
4. Background and Relative Source Contribution
to Chromium Exposure
4.1 Diet
4.2 Water
4.3 Air
5. Select Subpopulations
V. HAZARD ASSESSMENT
VI. LEVELS OF CONCERN
VII. REFERENCES
Michael Bolger, Ph.D., D.A.B.T.
Contaminants Standards Monitoring and Programs Branch, HFS-308
Division of Programs and Enforcement Policy
Office of Plant and Dairy Foods and Beverages
Clark D. Carrington, Ph.D., D.A.B.T.
Contaminants Standards Monitoring and Programs Branch, HFS-308
Division of Programs and Enforcement Policy
Office of Plant and Dairy Foods and Beverages
Curtis E. Coker
Special Assistant to the Director, HFS-301
Office of Plant and Dairy Foods and Beverages
Gregory M. Cramer, Ph.D.
Policy and Guidance Branch, HFS-416
Division of Programs and Enforcement Policy
Office of Seafood
Michael J. DiNovi, Ph.D.
Chemistry Review Branch, HFS-247
Division of Product Manufacture and Use
Office of Pre-Market Approval
Scott Dolan
Elemental Research Branch, HFS-338
Division of Pesticides and Industrial Chemicals
Office of Plant and Dairy Foods and Beverages
This document has been developed to satisfy requests from local and state officials for federal guidance regarding the public health significance of chromium in shellfish. (The term "shellfish" is used in a general sense throughout this document and is meant to include both molluscan bivalves and crustacea.) This document is designed to assist local and state health officials in their deliberations concerning the possible need to either issue consumption advisories or to close waters for fishing because of excessive chromium contamination. The contents of this document include sections on FDA's statutory authority, a public health statement, sampling techniques and trace element analysis, consumption and exposure information, hazard assessment, and a discussion of estimating levels of concern for local consumption advisories or water closures.
Chromium is a naturally occurring element that is distributed in the air, water, soil, and the earth's crust. The trivalent form and its salts are usually the most stable form of chromium and the main form found in plants and animals. Hexavalent chromium salts are less stable and more biologically reactive. High concentrations of chromium in the environment are due to industrial emissions, effluents from waste dumps, sewage sludges, fossil fuel combustion, incineration of municipal solids, and hazardous wastes. Virtually all foods contain chromium at levels up to 0.5 ppm wet weight. The estimated daily intake of chromium is 0.03 to 0.1 mg/person/day.
Chromium (III) is an essential trace element in humans. Approximately 1% of chromium in the
diet is absorbed. The low levels that are present in the diet are generally thought
to adequately supply nutritional needs for chromium, about 0.1 to 0.3 mg of inorganic
chromium/person/day. Cr (III) exposure has not been associated with any specific adverse effects, rather, a
deficiency of this element can be detrimental to human health. The National Academy of Sciences
recommends a daily intake level of trivalent chromium of 50-200 g/person/day.
Surveys of contaminants in shellfish conducted by FDA and the National Marine Fisheries
Service have found mean chromium levels ranging from 0.1 ppm up to 0.9 ppm (wet weight
basis). FDA has combined these survey results with nationally representative shellfish
consumption information to estimate the range of chromium exposures that is possible among
shellfish consumers. For individuals who chronically consume an average of 15 g/day of
molluscan bivalves (90th percentile intake over 14-days for consumers among survey
population) that have mean chromium levels of 0.4 ppm (the highest mean value found in the
NMFS survey), chromium intake will average 6 g/person/day. For people consuming an
average of 17 g/day of crustacean shellfish (90th percentile average intake over 14-days for
consumers among survey population) that contain mean chromium levels of 0.3 ppm, chromium intake will average 5 g/person/day.
Local patterns of shellfish consumption and/or the levels of chromium contamination may vary
from national averages. Hence, chromium exposures from shellfish in particular
regions may
also vary from values estimated using national figures. In order to decide whether local
chromium exposure levels are of concern, it is suggested that the estimated safe and adequate
dietary intake for chromium (III) (200 g/person/day) be used to calculate Levels of Concern,
either maximum permitted amounts of chronic shellfish consumption or maximum permitted levels of chromium contamination.
Although local figures for shellfish consumption or shellfish contamination would be most appropriate for evaluating local situations, reference to national figures may also prove useful. As an example, if it is assumed that total chromium exposure is derived solely from shellfish, it is calculated that the chromium level of concern for individuals consuming molluscan bivalves on a chronic basis at the 90th percentile average among eaters (15 g/person/day) would be 13 ppm. The corresponding consumption level of concern for individuals consuming molluscan bivalves with chromium levels equivalent to the highest average found in one of the national surveys (0.4 ppm) is 500 g/person/day. If other sources of chromium exposure are to be considered (e.g., relative source contribution including other dietary sources of chromium), then corresponding adjustments in the levels of concern will need to be made.
Purpose
Over the years, and particularly of late, concern has been raised regarding the public health significance of the presence of contaminants in shellfish in both fresh water and marine species. Local and state officials have repeatedly sought guidance at the federal level on these matters; in particular, the advice and position of the U.S. Food and Drug Administration (FDA) has often been requested. FDA is developing a series of guidance documents in an attempt to satisfy the requests for federal guidance. They are designed to assist local and state health officials in their deliberations concerning contaminants in shellfish and the possible need to either issue fish consumption advisories or to close waters for fishing. The term "shellfish" is used in a general sense throughout these documents and is meant to include both molluscan bivalves and crustacea.
Standards have been developed for those contaminants which have been identified as national problems (e.g. methylmercury). Guidance documents have been and will continue to be developed for contaminants which could cause health effects, based on the toxicity of the contaminant and potential exposure. These health effects generally have a low probability of occurring. In some localities, however, adverse health effects may occur under extreme conditions of exposure. Should such conditions exist or occur the information in this guidance document indicates how tolerable levels of shellfish consumption or contamination might be determined; however, it does not dictate an approach or decision regarding a particular contaminant in shellfish. These guidance documents have no statutory authority. They merely present the relevant scientific information on each contaminant. How this information is used is entirely up to public health officials who consult them and may in large part be determined by the particular circumstances of each case.
Based on conclusions reached from a meeting with representatives of state public health organizations, the decision was made not to develop a single advisory level. Instead, a broad guidance approach was developed to address the relevant information on a contaminant so that the information can be used as part of the overall determination of the public health significance of contaminants in shellfish.
Selection of Contaminants
The first guidance documents (for arsenic, cadmium, chromium, lead, and nickel) address contaminants chosen because they are most likely to occur and frequent concerns have been raised regarding their presence in shellfish. Concern about these elements is to be expected, since shellfish tend to accumulate elemental contaminants present in the environment.
Relevant Statutory Authority
The guidance documents were developed with a clear understanding of the statutory responsibilities of the Environmental Protection Agency (EPA) (e.g. Clean Water Act), the FDA, and the states. There is no intent to circumvent the statutory authority of any state or federal authority.
Scope
These guidance documents have been designed for use by public health officials at the federal, state and local level, other interested parties and members of the general public. These documents are being issued to present FDA's assessment of the current state of knowledge on specific contaminants and they will be revised when important new information becomes available. The agency requests and strongly encourages anyone with relevant information to add to these documents to contact the Office of Seafood at the address shown on the cover of this document.
Each guidance document begins with a public health statement much like that given in the toxicological profiles published by the Agency for Toxic Substances and Disease Registry (ATSDR). The sections that follow present information about sampling shellfish, analytical procedures for analysis of elemental contaminants in shellfish, consumption and exposure assessments, and conclude with a summary of toxicological and adverse effects of these contaminants. Each document identifies and summarizes the key literature describing the information, including the work of other health organizations (e.g toxicological profiles - ATSDR and environmental health criteria -International Program on Chemical Safety/World ealth Organization).
The purpose of the Federal Food, Drug, and Cosmetic Act (FD&C Act) is to ensure a safe nd wholesome food supply. The FD&C Act and other related statutes, including the Public Health Service Act, provide the regulatory framework under which the Food and Drug Administration assesses the effects of environmental contaminants on the safety of consumption of fish and shellfish (molluscan bivalves and crustacea). FDA has jurisdiction over foods that are intended for introduction into, or have been shipped in interstate commerce.
The basic provision of the Act dealing with poisonous or deleterious substances in food is section 402(a)(1). This section states:
- (a)(1) if it bears or contains any poisonous or deleterious substance
which may render it injurious to health; but in case the substance is
not an added substance such food shall not be considered
adulterated under this clause if the quantity of such substance in
such food does not ordinarily render it injurious to health;This section applies to all poisonous or deleterious substances, whether they are naturally occurring or added.
Section 402(a) (1) of the Act distinguishes between naturally occurring and "added" substances and sets different standards for each. Naturally occurring substances would adulterate a food only if they render the food "ordinarily" injurious to health. Added substances would adulterate the food if the food "may" be injurious to health.
The term "added" in this legal context is important. An added poisonous or deleterious substance is a substance that does not occur naturally in foods. A "naturally occurring poisonous and deleterious substance" is a substance that is an inherent, natural constituent of a food and is not the result of environmental, agricultural, industrial, or other types of contamination. When a naturally occurring, poisonous, or deleterious substance is increased to abnormal levels through mishandling or other intervening acts, it is regarded as an added substance.
Under conditions where an unavoidable contaminant occurs at a level that is of concern to FDA, FDA may establish a formal tolerance limiting the extent of allowable contamination of a food. Compliance with a tolerance is strictly determined on the basis of the results of analysis of commingled representative subsamples of edible portions taken from a fish shipment, not on the basis of a single fish. However, when toxicological data are scanty or conflicting, when additional data are being developed, or when other conditions are rapidly changing, FDA may choose not to establish a tolerance. Nevertheless, it may still be appropriate to take some regulatory action to control exposure to a contaminant. In such circumstances, FDA may consider developing guidelines or regulatory limits.
The authority of the FD&C Act extends only to fish and shellfish that are moving in interstate commerce. Accordingly, tolerances and guidelines are typically established on a national basis when it is judged that a national problem exists for a particular contaminant. Thus, guidelines are generally, but not always, tailored to national needs and national patterns of consumption. For example, consumption levels of fish on a national per capita basis are generally considerably less than those typical of sports fishermen or of individuals living near lake shores or coastal regions of the U.S. Nonetheless, the toxicity information {Reference Dose, (RFD) or Acceptable Daily Intake (ADI)} that is considered in the setting of national guidelines, may be useful to the states in establishing local controls or advisories on local shellfish consumption. If a potential local health threat exists, a state or locality may wish to issue warnings or provide guidance on the quantity of contaminated shellfish that may be safely consumed. Local authorities can utilize the available federal toxicity information and compare it with the level of the contaminant found locally and local shellfish consumption patterns to establish acceptable levels.
Chromium (Cr) is a naturally occurring element distributed in air, soil, water, and the earth's crust. It is an essential element which exists in all oxidation states from +II to +VI but only the trivalent Cr (+III) and hexavalent Cr (+VI) compounds are of practical importance. Trivalent (+III) chromium is usually the most stable state of chromium in nature and its salts are generally insoluble in water in the pH range of 4-11. Hexavalent chromium (VI) salts are less stable, quite soluble in water and more biologically reactive. Their tendency to be reduced to the trivalent state increases with decreasing pH. Cr (III) is the main form found in plants and animals. Forms Cr (O) and Cr (VI) arise almost entirely from industrial sources.
The principal industrial uses of chromium are in stainless steel production and chrome electroplating. Other commercial uses include leather tanning, printing, and production of dyes, pigments, primer paints, and wood preservatives. Chromium compounds are also used as slimicides in cooling towers and audio, video, and data storage. High concentrations in the environment are due to industrial emission, effluents from waste dumps, sewage sludges, fossil fuel combustion, incineration of municipal solids, and hazardous wastes. Virtually all foods contain chromium (III) at levels up to 0.5 ppm wet weight. The estimated daily intake is 0.03 to 0.1 mg/person/day. The daily human requirement is about 0.01-0.04 mg of organically complexed chromium or about 0.1-0.3 mg of chromium in an inorganic form.
In the general population the body burden of chromium is highest at birth and declines with age. The major routes of exposure are lung, gastrointestinal (GI) tract, and skin, with Cr (VI) taken up much more readily than Cr (III). The prominent route of exposure in occupational settings is the lungs. In humans, approximately 1% of Cr (III) in the diet is absorbed. Ingested Cr (III) is bound to plasma proteins. Chromium transported by blood is distributed to tissues and organs which have different retention capacities. The highest levels of chromium are found in the liver, kidneys, spleen, and lungs. The main route of chromium excretion is through the kidneys. Chromium (III) is an essential trace element in humans. It is required for maintenance of normal fat and cholesterol metabolism, and insulin and glucose homeostasis. Chromium deficiency is infrequent in humans and is usually limited to the elderly or to rare cases of patients subjected to prolonged parenteral nutrition. Chromium deficiency is associated with decreased glucose tolerance, some forms of diabetes, and cardiovascular diseases.
The low levels of chromium ubiquitously distributed in food and water are generally thought to adequately supply the nutritional demands for chromium. Dietary supplementation with Brewer's yeast has been used for the treatment of groups at risk, such as the elderly, malnourished children, or diabetics.
The toxicity associated with chromium results primarily from industrial exposure to the Cr (VI) compounds. Chromium (VI) compounds are classic skin irritants and sensitizers. Effects have been noted in occupationally exposed workers at air concentration levels as low as 0.1 mg/m3. Exposure to complex mixtures of Cr (VI) and Cr (III) compounds occurs in industrial plants where increased incidence of cancer has been reported, i.e., in the production of chromates, chrome pigments, or chromium plating plants. Chromium (VI) compounds may also cause adverse effects in the liver and kidney. Preliminary data indicate that Cr (VI) may cause cancer in animals at the exposure site, however, more data are needed to verify these findings. Chromium (III) compounds have not been associated with any specific adverse effects, rather, a deficiency of this element can be detrimental to humans. There is no evidence of carcinogenicity of trivalent chromium.
The U.S. National Academy of Sciences (NAS, 1989) recommends a daily intake level of
trivalent chromium of 50-200 g/day.
This daily intake figure was developed to be applied to
short term and chronic exposures and was not meant to be applied to incidences involving single daily exposures to chromium.
In this section methods for the determination of elemental contaminants in shellfish are examined. Necessary steps for shellfish analysis are outlined without repeating published methodologies. Specific analytical procedures are cited.
1. Sampling
Collecting, processing, preserving, and shipping primary samples are the critical steps required for generating valid analytical data. A detailed sampling plan for proposed specific sample collection sites should be developed before actual collection is started. The plan should include site locations, target species, target contaminants, sampling times, types of samples, and sample replication. Samples must be representative of the site or lot being studied. In addition, these steps must be conducted in a manner that preserves the integrity of the analyte(s) of interest and precludes inadvertent contamination (EPA, 1991). If sampling of processed shellfish products is required, specific sampling procedures can be found in the FDA Inspection Operations Manual (FDA, 1990).
1.1 Field Sampling Procedure
A minimum of 3 replicate composite samples from each sampling location is recommended for a representative site or lot. The shellfish collected should satisfy any legal requirements for harvestable size or weight or be of consumable or "market" size when no legal harvestable requirements are in effect. Selection of the largest animals is recommended if a worst-case exposure sampling is desired (EPA, 1991).
Animals used in composited samples should be of similar size with the total length (size) of the smallest animal having no less than 75 percent of the total length (size) of the largest animal. Composites should be composed of equal numbers of from 10 to 50 animals (depending on the species and size class being sampled) for a total minimum weight of 500 g of tissue homogenate. The relative difference (in percent) between the overall mean length (size) of replicate composites and the mean length (size) of any individual composite should be no greater than 10 percent (EPA In progress).
1.2 Laboratory Sample Preparation
Shellfish should be preserved with ice if they are not processed immediately. If shellfish are shipped or stored more than 24 h before processing, dry ice must be used. All laboratory samples should be prepared and analyzed, or frozen, as soon as possible after collection, preferably within 48 h. All instruments, work surfaces, and containers used in processing laboratory samples must be composed of materials that can be easily cleaned and that are not themselves potential sources of contamination. To avoid cross-contamination, all equipment used in sample handling should be cleaned before each test sample (EPA, 1991). Cleaning plastic equipment for trace element analysis has been studied and guidelines are given by Moody and Lindstrom (1977).
Equipment should be chosen to minimize contamination. Contamination may be minimized by using titanium, aluminum, quartz, TFE (tetraflouroethylene), polypropylene, or polyethylene utensils, and a glass blender or food processor with titanium or stainless steel blades and Teflon, polyethylene, or polystyrene gaskets (FDA, 1975). Stainless steel that is resistant to corrosion may be used if necessary. Stainless steel scalpels have been found not to contaminate mussel samples (Stephenson et al., 1979). However, other biological tissues (e.g., fish muscle) containing low concentrations of heavy metals may be contaminated significantly by any exposure to stainless steel (EPA, 1991). The predominant metal contaminants from stainless steel are chromium and nickel. Titanium utensils have been used successfully and are available commercially (Zeisler et al.,1988; Private Communication 1). Aluminum is also an option to consider, especially if it is not an element being studied. Titanium and aluminum each have the advantage of contaminating the sample with only one element. Quartz utensils are ideal but expensive. The analyst must know the elements of interest and their approximate levels in the species to be analyzed in order to make an informed decision about utensil selection.
Before shellfish are "shucked" (opened), the external shell surface should be thoroughly cleaned with brush and water to remove all sand, dirt, etc., adhering to the shell to prevent contamination of composite samples. After shellfish are shucked, the meat and liquor are carefully removed from the shell and collected to minimize incorporation of shell fragments and sand into the test sample. The presence of shell fragments or sand will complicate mineralization. Separation can be accomplished by transferring the meat and decanting the liquor, leaving sand and shell fragments behind. For analysis of canned, frozen, or otherwise processed products, the test sample should include meats, liquor, and any breading. Thaw frozen products prior to homogenization (McMahon and Hardin, 1968). Once shellfish are frozen, thawing of shellfish samples should be kept at a minimum during tissue removal procedures to avoid loss of liquids.
Comminute entire test sample in a glass blender or food processor to obtain a homogeneous mixture. When a food processor is used, adding dry ice successfully freezes the suspension and minimizes water separation. Precaution: If dry ice is used, check dry ice for interferences and store frozen test samples loosely covered overnight to allow for dissipation of carbon dioxide. Composite test samples should be homogenized to a paste-like consistency before portions are taken for analysis. Store prepared test samples frozen in glass jars with Teflon-lined lids or in Teflon containers. If analysis is not started immediately after homogenization, appropriate analytical portions may be weighed and stored frozen. This will eliminate the need to rehomogenize a thawed test sample.
2. Analytical Methodology
Review of the literature reveals that many inorganic analytical studies of shellfish have been prompted largely by a concern that abnormally high levels of toxic elements contaminate some of the world's shellfish growing areas (Marcus and Thompson 1986; Lytle and Lytle, 1982; Watling and Watling, 1982; May and McKinney, 1981; Micallef and Tyler,1989; Balogh, 1988; Eisenberg and Topping, 1984; Gault et al., 1983; Meeus-Verdinne, 1983; Favretto et al., 1981; Cooper et al., 1982).
This concern has focused mainly on elements of biological interest including antimony, arsenic, cadmium, chromium, copper, lead, manganese, mercury, molybdenum, nickel, selenium, tin, and zinc. Various techniques have been applied to analysis of shellfish; however, in the laboratories surveyed (Private Communications 2-5) routine shellfish analysis is conducted usually by using only a few methods. Most methods of shellfish analysis require mineralization of test portions. The digestion procedures can then be coupled with the determinative techniques presented in 2.2 of this section to form complete analytical methods.
2.1 Mineralization
Digestion procedures fall into one of two general categories, dry ash or wet ash. Dry ash digestions use a long, slow ashing step, usually performed overnight in a muffle furnace. The ashing process is completed by the addition of a small quantity of inorganic acid to the residue and evaporation on a hot plate. The residue is redissolved in acid and the solution is brought to volume with distilled or deionized water. Dry ash procedures can be found in the Association of Official Analytical Chemists (AOAC) method 972.23 (Helrich, 1990). Element loss during the ashing process is greater for dry ash procedures than for wet ash procedures. "Ashing aids" are often employed to prevent loss of the more volatile elements like arsenic and selenium (Maher, 1983; May, 1982).
Wet ash digestions are characterized by short ashing times (normally 3 to 4 h) and the use of acids (HCl, HNO3, H2SO4, HClO4). Wet ashing is performed by adding acid or an acid mixture to the test portion and boiling until digestion is complete. A variety of procedures have been developed using different types of digestion apparatus to retain volatile elements. The most common procedure is performed in beakers on a hot plate. The analytical portion is boiled with HNO3 or a mixture of HNO3 and HCl until digestion is complete (FDA, 1975; ASTM, 1986). Combinations of HNO3, HClO4, and H2SO4 have also been used for more efficient oxidation. Perchloric acid requires constant operator attention, specialized equipment (HClO4 hoods, fume traps, etc.), and safety precautions (Michie et al., 1978).
"Hot-block" digesters have been used for improved temperature control and their reflux capabilities (Agemian et al., 1980). "PTFE (polytetrafluoroethylene) bomb" digesters have been used because digestion can take place in a sealed vessel, thereby retaining volatile elements (Welz and Melcher, 1985).
Another wet ash approach that has been applied to fish analysis is microwave digestion (Schnitzer et al., 1988; Nadkarni, 1984; McCarthy and Ellis, 1991). This technique has been subject to extensive research and development since microwave technology was first applied to digestions (Abu-Samra et al., 1975; Barrett et al., 1978; Nadkarni, 1984; White and Douthit,1985; Kingston and Jassie, 1986, 1988; Burguera et al., 1986; Fernando et al., 1986). Current systems incorporate many features to improve digestion time, element recoveries, contamination, and safety. Improved recoveries can be achieved with systems operating under power-regulated control of pressure because these systems allow digestions to be completed without venting volatile elements. Sealed digestion vessels also reduce acid consumption and, in combination with Teflon construction, reduce contamination problems. Microwave digestion methods developed for shellfish do not require HClO4 to complete mineralization. Microwave digestion has been compared to some of the other digestion procedures (Blust et al., 1988).
Regardless of the digestion procedure selected, appropriate quality assurance and quality control guidelines need to be followed. These include the use of contamination control, digestion blanks, spiked test portions, replicate analyses, an appropriate standard reference material (e.g., National Institute of Standards and Technology: Oyster or Bovine Liver), and recovery calculations (Boyer and Horwitz, 1986; Jones, 1988).
2.2 Determinative Techniques
Selection of a determinative technique is often dictated by available equipment and quantitation requirements. Ease of operation, number of analyses, and familiarity of personnel with techniques are also influential factors. For these reasons only a few methods developed for shellfish analysis are used for routine testing. Spectrometric techniques are most commonly used and include flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry (GFAAS), and inductively coupled plasma-atomic emission spectrometry (ICP-AES) (see Table 1).
FAAS is often used to determine many elements in shellfish analysis because it is easy and affordable (Private Communications 2-5). The American Society for Testing and Materials (ASTM) method D3559 (ASTM, 1986) and the American Public Health Association (APHA) method 303 (APHA, 1986) both use FAAS. FAAS has been combined with high-performance liquid chromatography (HPLC) for the study of metal ion speciation in biological systems. Information about the distribution of metal ions in biological extracts can be used to estimate exposure of an animal to chemical toxins, and to estimate the relationship between chemical form and bioavailability (Guy, 1985).
FAAS has been applied to two methods to improve detection of some elements. First, measurement of arsenic and lead has been improved by on-line generation of volatile hydrides with hydride generation-AAS (HG-AAS) (Holak, 1969). In applications of hydride generation to fish analysis, (Agemian and Thompson, 1980; Julshamn et al., 1982; Cutter, 1985; Maher, 1982, 1986; Madrid et al., 1988) the enhancement of detection limits ranged from a factor of 5 to a factor of over 500 (see Table 1). Hydride generation (HG) has also been coupled with GFAAS (Willie et al., 1986; Sturgeon et al., 1986), direct current plasma-AES (DCP-AES) (Panaro and Krull, 1984), and ICP-AES (de Oliveira et al., 1983; Montaser and Golightly, 1987). HG-AAS has been coupled with HPLC for determination of inorganic and methylated arsenic species in marine samples (Maher, 1981).
GFAAS has been used for measurement of selected elements when FAAS determination limits were insufficient for shellfish analysis (Cruz et al., 1980;Serra and Serrano, 1984). Clearly, GFAAS is more sensitive than FAAS although GFAAS analysis time is longer. The main problems with GFAAS shellfish analysis are matrix and spectral interferences. Deuterium arc and Zeeman-effect background corrections have been applied to reduce spectral interference in shellfish analysis. While deuterium arc background correction is plagued by spectral interferences, Zeeman-effect background correction appears to be satisfactory for routine analysis of marine biological tissue (Welz and Schlemmer, 1986; McMahon et al., 1985). Various "matrix modifiers" (organic and inorganic reagents) have been used to reduce matrix effects. Molybdenum, lanthanum, and ammonium dihydrogen phosphate have been used as matrix modifiers for shellfish analysis (Poldoski, 1980; Mckie, 1987). Solvent extraction is another approach taken to minimize matrix effects (Stephenson and Smith, 1988; Harms, 1985).
Solid sampling has been developed for GFAAS to increase relative sensitivity by avoiding the large dilution factors required in the sample dissolution. Solid sampling also eliminates contamination and/or loss of analyte resulting from dissolution. Solid sampling has not been widely used for shellfish analysis because of possible interference by very large background matrix absorbance (Chakrabarti, 1979; May and Brumbaugh, 1982). A complete analysis by GFAAS can be found in ASTM method D3559 (ASTM, 1986).
ICP-AES has also been used for routine elemental analysis of shellfish (Grant and Ellis, 1988). Sequential or simultaneous mode ICP-AES allows rapid analysis, dramatically improving throughput. Detection limits in ICP-AES are generally the same as those in FAAS except for elements that are difficult to atomize. Such elements have lower ICP-AES detection limits because of the higher temperature of the plasma (see Table 1). A complete analysis by ICP-AES can be found in the EPA's water method 200.7 (EPA, 1979).
Although not widely used for routine shellfish analysis, techniques have been developed using voltammetry for trace element determination (ASTM, 1986; Adeloju and Bond, 1983; Breyer and Gilbert, 1987), polarography (Lemly, 1982), ICP-MS (Munro et al., 1986; Beauchemin et al., 1988; Park et al., 1987), HPLC with electrochemical and spectrophotometric detection (Bond and Nagaosa, 1985), and neutron activation analysis (NAA) (Zeisler et al., 1988; LaTouche et al., 1981; DeSilva and Chatt, 1982; Chisela and Bratter, 1986).
Regardless of the analytical method chosen, sound scientific analytical principles must be followed. All methods used by a laboratory must be validated by the laboratory prior to routine sample analysis. The detection and quantitation limits, and accuracy and precision of each method must be assessed and documented to be sufficient for reliable quantitation at or below the level of interest for each metal. All analytical methods used routinely for the analysis of shellfish should be documented thoroughly; formal standard operating procedures (SOP's) are preferred. A published method may serve as an analytical SOP only if the analysis is performed exactly as described. Analytical SOP's should be followed as written (EPA, 1991).
3. Quality Assurance/Quality Control (QA/QC)
Initial demonstration of laboratory capability and routine analysis of appropriate QA/QC samples to document data quality and to demonstrate continued acceptable performance is essential. QA/QC requirements should be based on specific performance criteria, or control limits, for data quality indicators, such as accuracy and precision. Typically, control limits for accuracy are based on the historical mean recovery plus or minus three standard deviation units, and control limits for precision are based on the historical standard deviation or coefficient of variation (or mean relative percent difference for duplicate samples) plus three standard deviation units. Some recommended QA/QC procedures include: instrument calibration and calibration checks, assessment of method detection and quantitation limits, assessment of method accuracy and precision, routine monitoring of interferences and contamination, regular external QA assessment of analytical performanceinterlaboratory comparison programs, appropriate documentation, and reporting of data (including QA/QC data) (EPA, 1991).
Table 1. Quantitation Limits (
ICP-AES FAAS GFAAS(f) Solution Hydride Solution Hydride Element neb.(b) gen.(c) neb.(d) gen.(e)
As 0.5 0.008 10.0 0.03 0.01 Cd 0.05 0.007 0.0005 Cr 0.3 0.20 0.003 Ni 0.2 0.3 0.02 Pb 0.8 0.03 0.3 0.003 0.005 (a) Quantitation limits (10 sigma) were estimated from instrumental detection limits (3 sigma), and a 5 g test portion in 50 ml of test solution was assumed. (b) Values for pneumatic nebulizer/ICP-AES are taken from Applied Research Laboratories literature on Model 3580 OES. (c) Values are reported in Montaser and Golightly (1987). (d) Values are taken from Varian literature on Models AA-1275 and AA-1475 best value was selected for either C2H2-air or C2H2-N2O flame. (e) Value for arsenic are reported in Robbins and Caruso (1979); value for lead in Ikeda et al. (1982). (f) Values are taken from Varian literature on Model Spectra AA-300 (nominal 20 uL injection).
The following sections provide estimates of chronic shellfish intake as well as estimates of chromium exposures resulting from chronic shellfish consumption. In addition, estimates of chromium exposure are provided for background sources, both dietary (i.e. non-seafood) and non-dietary sources.
1. Shellfish Intake
The frequency of shellfish eating occasions has been tabulated in the Market Research Corporation of America (MRCA) 14-day survey, (5-Year Menu Census, 1982-87 (MRCA, 1988). The MRCA reports that only 13% of the surveyed population consumed crustaceans and only 4.8% of the surveyed population (25,726 individuals, 2+ years) consumed molluscan bivalves. Using standard portion sizes from the USDA's 3-day National Food Consumption Survey (NFCS, 1977-78) (Paoet al., 1982) we estimate the 14-day-average mean and 90th percentile daily intakes of molluscan bivalves. These are presented in Table 2. The intakes for crustacean shellfish are presented in Table 3.
Table 2. 14-Day average intake of molluscan bivalves, grams/person/day,
for eaters only.
Age Group Mean 90th Percentile
2+ years (all ages) 10 15
2-5 years 4 8*
(male/female)
18-44 years** 12 18
(male/female)
* Estimated value. Reliable data are not available in the MRCA
survey. The 90th percentile value is estimated to be twice
the mean (WHO, 1983).
** USDA portion size for 33-44 year age group used in the
calculation. This age subgroup has the highest consumption
of any subgroup in the 18-44 year range.
Table 3. 14-Day-average-intake of crustacean shellfish,
grams/person/day, for eaters-only.
Age Group Mean 90th
Percentile
2+ years (all ages) 9 17
2-5 years 5 10
(male/female)
18-44 years* 9 19
(male/female)
* USDA portion size for 33-44 year age group used in the
calculation. This age subgroup has the highest consumption
of any subgroup in the 18-44 year range (Pao et al., 1982).
2. Chromium Concentrations in Shellfish
Three studies cited herein provide considerable data on chromium levels in shellfish. Although none of these studies characterized the valence state of the chromium in the shellfish, it is assumed, since chromium is normally present in biological systems entirely as Cr (III), that the levels reported are for Cr (III).
The National Oceanic and Atmospheric Administration (NOAA) mussel watch project progress report (NOAA, 1989) indicates that none of the mussels and oysters in the 169 sites examined in 1988 exhibited an average chromium concentration in excess of 0.25 ppm wet weight {the following factors for converting dry weight concentrations reported by NOAA to wet weight values were used: Crassostrea virginica, 0.124; Mytilus edulis, 0.121; (Private Communication 7, 1990).}
In 1985-86 the FDA surveyed the levels of chromium in softshell clams (Myaarenaria), hardshell clams (Mercenaria mercenaria), Eastern oysters (C. virginica), and Pacific oysters (C. gigas) (S. Capar, FDA, Division of Contaminants Chemistry, unpublished data). The shellfish samples were harvested from approved waters in 20 coastal states (all coastal states except Alaska and New Hampshire), although not all species were sampled in all states. The results of that survey are presented in Table 4.
Table 4. Results of the 1985-86 FDA shellfish survey for chromium.
Sample Mean chromium level(1) Range Species Size (
shell 67 0.36 0.078-0.57 Clam, softshell 59 0.89 0.25-1.4 Oyster, Eastern 100 0.71 0.047-2.1 Oyster, Pacific 40 0.30 0.2-0.5 Clams, overall 0.63 Oysters, overall 0.50 (1) Wet weight basis.
In 1978, the National Marine Fisheries Service (NMFS) published the results of a survey on trace elements in fish (Hall et al., 1978). Chromium levels in several species of shellfish are presented in Table 5.
Table 5. Results of the NMFS survey of trace elements in the
fishery resource for selected shellfish.
Range of Mean
Sample chromium levels(1,2)
Species Size (g/g)
Clam, hardshell 141 0.3-0.4
Clam, softshell 18 0.2-0.3
Oyster, Eastern 150 0.3-0.4
Oyster, Pacific 70 0.3-0.4
Average of the range of mean 0.3-0.4
chromium level for
molluscan bivalves
Crab, blue, body/claw 54 0.2-0.3
Crab, dungeness, body/claw 8 0.2-0.3
Lobster, American, tail 2 0.1-0.2
Lobster, spiny, Atlantic, tail 40 0.1-0.2
Lobster, spiny, Pacific, tail 5 0.1-0.2
Shrimp, ocean 10 0.2-0.3
Shrimp, pink (northern) 61 0.2-0.3
Average of the range of mean 0.2-0.3
chromium levels for
crustaceans
(1) Wet weight basis.
(2) Shellfish from a single survey site formed a sample.
Chromium content was averaged for each sample.
Each species was sampled at many sites. This table
reports the range of the mean chromium levels that
encompassed all samples.
Chromium levels reported in the NMFS survey are slightly lower than those reported in the FDA survey. Chromium results from the NOAA Mussel Watch survey are in general agreement with chromium content values for molluscan shellfish presented in the NMFS survey. In general, greater numbers of each species were sampled in the NMFS surveys than in the FDA survey. The FDA survey data, however, were gathered seven years or more after the NMFS survey. The data do not allow conclusions to be drawn about trends in contamination levels or about the validity of any survey. Because the two NOAA studies are in close agreement, we believe it is acceptable to use the NMFS trace element survey data in estimating consumer exposure. The NMFS is beginning a resurvey of trace metals in marine organisms and the results of this survey may delineate any trend in chromium contamination in marine organisms.
3. Chromium Exposure from Shellfish
Using information on chronic shellfish consumption and typical levels of chromium in shellfish, it is
possible to estimate chromium intake on a chronic basis for consumers of shellfish.
According to the MRCA survey, only 13% of the population eat crustacean shellfish, and only 4.8% of the population
eat molluscan shellfish. Assuming that mean chromium levels range from
0.3 g/g (ppm) to 0.4 g/g for molluscan shellfish and from
0.2 g/g to 0.3 g/g for crustacean shellfish, consumer
exposures (for eaters only) are presented in Tables 6 and 7, below.
Table 6. Molluscan bivalves - chronic chromium intake for specified levels
of contamination, g/person/day
Contam. at 0.3 ppm Contam. at 0.4 ppm
Age Group, Yrs. Mean 90th Mean 90th
Percentile Percentile
2+ (all ages) 3 5 4 6
(male/female)
2-5 1 2* 2 3*
(male/female)
18-44 4 5 5 7
(male/female)
* Estimated value. Reliable data are not available in the MRCA
survey. The 90th percentile value is estimated to be twice
the mean (WHO,1983).
Table 7. Crustacean shellfish - chronic chromium intake for specified
levels
of contamination, g/person/day
Contam. at 0.2 ppm Contam. at 0.3 ppm
Age Group, Yrs. Mean 90th Mean 90th
Percentile Percentile
2+ (all ages) 2 3 3 5
(male/female)
2-5 1 2* 2 3*
(male/female)
18-44 2 4 3 6
(male/female)
* Estimated value. Reliable data are not available in the MRCA
survey. The 90th percentile value is estimated to be twice
the mean (WHO, 1983)
4. Background and Relative Source Contribution to Chromium Exposure
4.1 Diet.
Trivalent chromium is an essential trace element nutrient for man. The element is required in amounts of 50-200 micrograms per day (NAS, 1989). Efficient glucose metabolism in humans requires trivalent chromium to form an antidiabetogenic, or glucose tolerance, factor.
Kumpulainen, et al. (1979) analyzed 28 selected daily diets of different composition for a human metabolic diet study and found the diets provided 25-224 g chromium per day (mean value 76 g/day). Anderson (1986) has reported that in the United States individuals tend toward chromium deficiency because of the low level of chromium in the diet. Polansky, et al. (1990) reported that dietary chromium intake in the U.S. is suboptimal, with roughly 25% of daily diets containing less than 40% (<20 g/day) of the minimum estimated safe and adequate daily intake (ESSADI) of 50 g chromium per day. The National Research Council reported that the mean daily dietary chromium intake in the United States is 62 g/day (NRC, 1980), an observation that tends to support the contention that Americans are minimally fulfilling their requirement for chromium. The richest sources of dietary chromium are from meats, mollusks, crustaceans, and unrefined sugar. Finfish are a poor source of dietary chromium.
4.2 Water.
The chromium in uncontaminated, unprocessed drinking water is primarily trivalent. There can be some hexavalent chromium in drinking water as a result of the production, use, disposal, and transport of hexavalent chromium compounds. The oxidation of chromium as a by-product of the chlorination and aeration of drinking water, results in the production of some hexavalent chromium. WHO (1988) indicates that drinking water from municipal water supplies does not contribute more than a few micrograms of chromium to the daily human intake. The contribution of chromium from drinking water to the body burden is considered insignificant in comparison to total chromium exposure from the diet.
4.3 Air.
WHO (1988) indicates that chromium occurs in the air of non-industrialized areas in concentrations of less than 0.1 microgram/m3. Chromium-related industries and every combustion process, including forest fires, emit chromium into the air.
The American Conference of Governmental Industrial Hygienists (ACGIH) lists adopted Threshold Limit Values (TLVs) for the commonly occurring oxidation states of chromium in the work environment (ACGIH, 1987). The TLV-Time Weighted Average (TWA), for chromite ore processing (chromate as chromium) and for certain water-insoluble chromium (VI) compounds (as chromium) is 0.05 mg/m3 of air. ACGIH defines TLV-TWA as the time-weighted average concentration for a normal 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect.
5. Select Subpopulations
The preceding exposure estimates for chromium intake from shellfish consumption are based on nationally representative food consumption surveys. These surveys may not be suitable for estimating exposures to particular subpopulations or individuals residing in specific regions of the country. State or local organizations will want to tailor estimates to their specific needs.
In addition to the nationwide food consumption surveys mentioned previously {Market Research Corporation of America (MRCA) 14-day Survey; USDA 3-Day National Food Consumption Survey (USDA-NFCS)}, the National Purchase Diary (NPD) survey presents a 14-day survey covering the continental United States (TRF, 1975).
Several other food consumption databases are also available for use in preparing estimates of exposure. Although none have the national character of the MRCA, NPD survey, or USDA-NFCS, they do address either the consumption of specific types of food (e.g. fish, shellfish), or they reflect the consumption patterns and habits of regional areas or of specific groups (e.g., fishermen). Some available databases, along with selected shellfish consumption values, are listed in Table 8, below.
Table 8: Shellfish Consumption
Seafood Consumption Level Population Source of the Data Category (g/day) All 5 (availability(a)) Entire U.S. NMFS "Fisheries of the U.S." Shellfish Series (1986)(b) 5 (average) Persons Earning NMFS (1981)(c) More than $15,000 per Year 9 (average) Shellfish-Eaters 1977-1978 Menu Census(d) 16 (90th percentile) Shellfish-Eaters 1977-1978 Menu Census(d) 30 (availability(a)) Shellfish-Eaters NMFS "Fisheries of the U.S." Series (1986)(b) Clams 1 (average) New Englanders NMFS (1981)(c) 22 (95th percentile) Texans 1973-1974 Tuna Institute Survey(e) Oysters 0.5 (average) Persons Earning NMFS (1981)(c) more than $15,000 per year 21 (95th percentile) Californians 1973-1974 Tuna Institute Survey(e) (a) Total availability of edible shellfish "meat" (excluding bones, viscera, shells), fresh, frozen and canned. (b) C. Lewis, FDA, in memo to I. Boyer, FDA, "Estimating a Level of Concern for Cadmium in Shellfish," 10-26-88. (c) Hu, T.-W., (1985). (d) Market Research Corporation of America (MRCA) as reported by C. Lewis, FDA, in memo to I. Boyer, FDA, "Estimating a Level of Concern for Cadmium in Shellfish," 10-26-88. (e) Tuna Research Foundation (1975), Seafood Consumption Study, National Purchase Diary Panel, Inc., Schaumburg, IL.
It is important to note that the level of consumption, and thus the level of contaminant intake, varies from survey to survey. The variation is controlled by several factors, among which are:
Finally, we note that in some circumstances it may be difficult or impossible to find a survey that adequately addresses a particular public health problem. In this case, the best choice may be to initiate a survey that will be specifically designed to address the question.
Chromium is a polyvalent metal that occurs most frequently as either Cr(III) or Cr (VI). We generally accept that only the commonly occurring oxidation states have biological importance. Chromium (II) is relatively unstable, being rapidly oxidized to Cr(III). It is unlikely that chromium (III) could be oxidized to chromium (VI) in vivo because the oxidation potential of Cr(III) to Cr(VI) is high. The Cr(VI) form, most frequently bound to oxygen, is a strong oxidizing agent. Human saliva and gastric juice will reduce some hexavalent chromium to trivalent chromium. Organic reducing matter in water readily reduces hexavalent to trivalent chromium.
The acute, subchronic, and chronic toxicity of chromium and its compounds by any route of exposure will depend in varying degrees upon oxidation state, solubility, and other physicochemical properties. In general, Cr(VI) compounds are more toxic than Cr(III) since the hexavalent form can pass through the cell membrane with greater ease and the Cr VI compounds are also more oxidative. The toxic manifestations of chromium exposure are apparently determined by the bioavailability and biochemical interactions of specific chromium compounds, rather than by chromium per se. (Katz, 1991). Very little is known concerning the biological mechanisms leading to the conversion of Cr VI into Cr III compound within the cell.
In most instances gastrointestinal (GI) absorption of ingested Cr(VI) compounds is greater than GI absorption of Cr(III) compounds, except for Cr(III) glucose tolerance factor. Human saliva and gastric juices reduce some hexavalent chromium to trivalent chromium, which crosses membranes with difficulty, with consequent poor gastrointestinal absorption. Once absorbed, there is nearly complete urinary excretion of chromium.
The kidney is the principal route of excretion of nearly all ingested chromium compounds. The form in which chromium is excreted has not been completely elucidated. Exposures of sufficient intensity to some chromium compounds produce kidney and liver damage, internal hemorrhage, dermatitis, and respiratory problems. Human lung tissue traps inhaled trivalent chromium compounds in the form of small particles within the respirable range. With the exception of the lungs, tissue levels of chromium decline with age. The pharmacokinetics of chromium and its compounds depends upon oxidation state, solubility, and other physicochemical properties. More pharmacokinetic studies are needed to establish the precise role of these factors.
There is no evidence of carcinogenicity of Cr(III) compounds or of elemental chromium by repeated ingestion in humans or animals. Results of human epidemiological studies associate prolonged, repeated inhalation of relatively high concentrations of certain Cr(VI) compounds, especially those of low water solubility, with induction of cancer of the respiratory tract. These and other studies do not identify a definite form of chromium as the proximate human lung carcinogen. Strong evidence suggests that calcium and zinc chromates are human carcinogens and that chromates of lead and strontium are carcinogenic in animals. Evidence also suggests that water soluble chromates in general may be more potent carcinogens than those with low solubility (Langard 1989, 1990). Chromium (VI) is a very broad acting genotoxic agent as evidenced by its ability to directly induce lesions as well as to indirectly generate oxygen radicals and reactive intermediates. Chromium is positive in almost every genotoxic assay in which it has been tested (Costa, 1991). Chromium (VI) has been shown to produce a variety of lesions in the DNA of mammalian cells including single-strand breaks, alkali-labile sites, DNA-DNA and DNA-protein crosslinks.
Trivalent chromium is an essential element required for normal energy metabolism. Animal studies have shown that it is required for normal glucose metabolism in that it acts as a cofactor for insulin via a mechanism which remains to be elucidated. The toxicity of Cr(III) is quite low, either on an acute or chronic basis. The few chronic studies (mice and rats) that have been performed with Cr(III) have shown no adverse effects with high doses in either drinking water or the diet.
The National Academy of Sciences (NAS 1989) gives estimated safe and adequate daily dietary
intakes (ESADDIs) of chromium of 20-80 g and 30-120 g for children of 1-3 and 4-6 years of
age, respectively, and 50-200 g for children of 7-11+ years of age and adults. This range is based
on the absence of chromium deficiency in the majority of the U.S. population whose average daily
dietary consumption is 50 g. The upper limit of the range, 200 g/day is based on several
human studies which showed that chronic dietary intake of Cr(III) at this level does not result in
adverse effects. This daily intake figure was developed to be applied to short term and chronic
exposures and was not meant to be applied to incidences involving single daily exposures.
The Environmental Protection Agency (EPA) established the maximum contaminant level (MCL) of total chromium in drinking water as 0.1 mg/l which was based on a maximum contaminant level goal (MCLG) of the same magnitude. The MCLG was developed from health effects information on Cr(VI) (EPA, 1991a). The EPA has also established a reference dose (RfD) for Cr(III) of 1 mg/kgbw/day. The RfD was derived from a long term feeding study (Ivankovic and Preussman, 1975) in rats which used high doses (up to 5% of the diet) of chromium oxide. The study failed to detect adverse effects and, as a result, neither a no-observed-effect-level nor a lowest-observed-effect level was identified. The confidence in the RfD is low, particularly because the absorption of insoluble chromium salts is quite low (less than 1%) (IRIS, 1993). Although EPA, in its guidelines for assessment of carcinogenic risk, may classify repeatedly inhaled Cr(VI) as a human carcinogen, there are inadequate data to conclude that chromium is carcinogenic via repeated ingestion. Accordingly, EPA deals with chromium as "not classified," a category for agents with inadequate animal evidence of carcinogenicity.
The World Health Organization (WHO) indicates that chromium occurs in the air of nonindustrialized
areas in concentrations of less than 0.1 g/m3 (WHO, 1988). Chromium industries and every
combustion process emit chromium into the air. The American Conference of
Governmental Industrial Hygienists (ACGIH), lists adopted Threshold Limit Values (TLV) for the commonly
occurring oxidation states of chromium in the work environment (ACGIH 1987). The TLV-Time
Weighted Average, TWA, for chromite ore processing (chromate), as chromium and for certain
water-insoluble chromium (VI) compounds (as chromium) is 0.05 mg/m3 of air. ACGIH defines TLV-TWA
as the time-weighted average concentration for a normal 8-h workday and a 40-h workweek, to which
nearly all workers may be repeatedly exposed, day after day, without adverse effect.
WHO (1988) discusses at some length dermal exposure to and effects on human skin of chromium and its compounds. The major problems of dermal exposure to Cr(VI) are irritation dermatoses, or ulcers (corrosive reactions), often called chrome holes or chrome sores. These occur among workers exposed to high concentrations of Cr(VI) compounds. Ulcers do not result from contact with Cr(III) compounds. There is no evidence that the ulcers undergo malignant transformation. Chromium is a skin sensitizer. Opinion is divided about the role of the oxidation state of chromium as a causal agent in allergic contact dermatoses. Patients with chronic dermatitis sometimes experience photosensitivity. Occupational dermal exposure to chromium compounds can result in percutaneous absorption.
WHO (1988) also reports that prior to 1982 perforation of the nasal septum was one of the main chronic effects of exposure in workers in contact with chromates and chromic acid. Ulcers were noted in these workers and a loss of the senses of smell and taste. The introduction of control measures caused the rate of nasal septum perforation to drop appreciably.
Summary.
Salient features of the general toxicology of chromium and its compounds are:
The following section illustrates how levels of concern, either permitted amounts of chronic shellfish consumption or permitted levels of contamination, can be determined using information on the maximum estimated safe and adequate dietary intake (ESADDI) of trivalent chromium. For the purpose of this illustration, it is assumed that total chromium (III) exposure is derived solely from shellfish. This approach leads to estimates of the maximum permitted levels of either shellfish intake or levels of chromium (III) contamination in the shellfish. If other sources of chromium exposure are to be considered (e.g., relative source contribution), then corresponding adjustments in the levels of concern will need to be made.
The following equations illustrate how the maximum estimated safe and adequate dietary intake
(ESADDI) of trivalent chromium (200 g/person/day for children 7-11 years and adults) can be
combined with information on either shellfish consumption or chromium (III) levels to estimate the
corresponding levels of concern of either shellfish contamination or shellfish intake. Estimates of
levels of concern for younger age groups (e.g., 1-3 or 4-6 years) should be
based on ESADDIs for the appropriate age category.
ESADDI = Cr (III) level x Daily intake of Shellfish
As an example, the Cr (III) level of Concern is estimated for individuals in the 2+ years age group consuming molluscan bivalves on a chronic basis at the 90th percentile level (15 g/p/d, see Table 2).
Cr (III) Level of Concern = {200 g/p/d} / {15 g/p/d} = 13 g/g
For molluscan bivalves with Cr (III) levels corresponding to the highest mean concentration reported in the 1978 NMFS survey (see Table 5), the corresponding molluscan bivalve consumption level of concern is calculated as follows:
Consumption Level of Concern = {200 g/p/d} / {0.4 g/g} = 500 g/p/d
The following tables present a number of plausible levels of concern, either consumption or concentration, that could be used in the assessment of the potential impact of chromium on human health through exposure from shellfish. For reference, the following values should be compared with shellfish intake and Cr (III) contamination figures presented in Section IV.
Table 9. Consumption Levels of Concern for Chromium (g/p/d)*
Molluscan Bivalves 500 Crustaceans 667 * Derived from the ESADDI and the highest mean concentration for total chromium (see Table 5) reported in 1978 NMFS survey.
Table 10. Chromium Levels of Concern in Molluscan Bivalves (
Age Group Mean 90th Percentile
2+ years (all ages) 20 13 18-44 years 17 11 (male/female) * Derived from the ESADDI and intake figures for molluscan bivalves presented in Table 2.
Table 11. Chromium Levels of Concern for Crustacean Shellfish (
Age Group Mean 90th Percentile
2+ years (all ages) 22 12 18-44 years 22 11 (male/female) * Derived from the ESADDI and intake figures for crustacean shellfish presented in Table 3.
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This Guidance document represented current agency thinking in regards to the available science at the time it was issued. It no longer represents the current state of science and is presented here for the historical record only.