Even though more detailed information regarding environmental history, environmental monitoring, biologic monitoring, risk communication, and risk assessment goes beyond what a primary health care provider will realistically know and do in the midst of a busy practice setting, this information is provided to help with understanding the role of others and communication with others (e.g., staff at the state or local health department, at the poison control center, at ATSDR, at the Association of Occupational and Environmental Clinics' Pediatric Environmental Health Specialty Units [PEHSUs], and experts at other organizations). It also gives a better understanding of what is involved in doing a comprehensive pediatric environmental medical evaluation.
The exposure history provides rough-estimate information about dose; the information rarely reflects the accurate quantitative value. Although the beliefs and concerns of the person providing the history can sometimes skew estimates of exposure, the interview usually successfully frames the boundaries of likely exposures. Reference to the scientific literature or the experience of specialists, such as industrial hygienists, might also provide reasonable estimates of dose based on monitoring done in similar situations. For example, knowing that a child lives in a house built in 1940 and that throughout the first 3 years of his life his father actively scraped, sanded, and repainted interior wood trim vividly points to potentially substantial
lead exposure of the child. Similarly, if a father brings a pound of mercury home from work as a toy for his children, and it is known that this mercury spilled on a shag rug, an industrial hygienist can roughly predict the mercury air concentrations. This exposure information points the child health care provider directly to the appropriate biologic tests to measure the absorbed dose.
Environmental monitoring sharpens exposure estimates when the history is vague, when biologic tests of absorbed dose are not available, and when the effectiveness of environmental mitigation activities is being assessed. Monitoring allows a measurement of a contaminant's concentration in a medium (e.g., air, soil, water, or food). Some tests might serve as indicators of exposure to other agents of concern. For example, water might be tested for coliforms as an index of exposure to other pathogenic fecal contaminants. Alternatively, monitoring might focus directly on the substances of concern, such as lead concentration in paint. As with any laboratory test, the physician, with the help of those with special expertise (e.g., environmental medicine doctors and toxicologists), should be able to interpret measures of environmental contaminants with knowledge of the potential for misleading results. When doing environmental monitoring, consider the following basic considerations:
Laboratory certification to perform the test. (Note: Both EPA and OSHA certify laboratories for specific contaminants. Contact the environmental division of your health department for further information.)
Qualifications of the person performing the sampling. (Incorrect field techniques can invalidate the results.)
Appropriateness of the test. (The child health care provider needs to have some idea of the chemical for which the test is being done [e.g., using a test to check for carbamate pesticide on a wipe sample in a house is meaningless if the pesticide used was a pyrethrin].)
Inclusion of typical and worst-case exposure scenarios in the sampling. (A first-flush sample of tap water from lead pipes will contain higher amounts of lead than a sample taken after the tap has run for 60 seconds. Air monitoring done 1 month after a fuel oil spill in a basement will not accurately reflect the potential for exposure during the first few days after the spill.)
Relevance of location of sample to the exposure area. (An elevated
radon level in a crawl space might have little health significance as long as the radon level in the living area is low.)
Level of concentration: average or peak. (Peak exposures to mold spores are more significant as a sensitizer than cumulative, average exposures.)
Using the monitoring results plus certain estimates (e.g., how much air children of a specific age breathe in a minute or how much soil they might ingest in a day), risk assessors in government agencies, including state health departments, can assist the child health care provider calculate dose estimates.
Biologic monitoring gets closest to the ultimate question of internal dose estimation: Has this patient absorbed sufficient amounts of a toxicant to cause harm? Knowledge of the metabolism, distribution, and excretion of a toxicant dictates the appropriate time and biologic fluid or tissue sample to obtain for testing. Most commonly, blood components and urine are tested. Biologic testing might do the following:
Directly measure a toxicant such as blood
lead or urine mercury.
Measure a metabolite of a toxicant, such as urine hippuric acid, as an indicator of
toluene absorption.
Measure an effect of the interaction of a toxicant with the host's biochemistry, such as carboxyhemoglobin as a measure of carbon monoxide exposure.
Indirectly measure the absorption of a toxicant by assessing the toxicity of a body fluid, such as testing carcinogen absorption in the urine. This is done with the Ames test, which detects compounds that are mutagenic. The test uses a strain of Salmonella that is auxotrophic for histidine (i.e., it cannot grow on a minimal media without added histidine).
Measure effects on target organs, such as elevated liver enzymes in a child exposed to a hepatotoxin. [Note: To avoid incorrect conclusions, the physician must interpret biologic tests with attention to the toxicokinetics of the specific contaminant of concern, particularly the half-life and distribution of the toxicant into different body partitions, such as bone, fat, and blood. For example, a plasma acetylcholinesterase level reflects organophosphate exposures within the last few days, whereas a red blood cell acetylcholinesterase level might indicate exposures dating back several months.]
Characterize the significance of exposure.
In the final phase of the evaluation, the clinician decides whether the identified environmental exposures are related to the presenting illness or are likely to cause a future health problem.
After a careful physical examination of the child, a conclusion is reached by answering several questions.
For the well, but exposed child and/or worried parent:
Have the identified environmental exposures been associated with health effects in people? If so, how convincingly?
How does the dose compare with known dose-response relationships?
What are existing exposure standards? Note that occupational standards should not be considered protective of children. Whenever possible, environmental standards should be used as benchmarks.
If standards do not exist, is there any available published information on human exposures?
If no relevant human data exist, but animal data suggest a risk, consultation with a toxicologist or pediatric environmental medicine specialist should be obtained.
What factors might increase or decrease the patient's susceptibility?
What other community or home exposures might contribute to an adverse health effect?
For the sick child:
How specifically can the medical problem be defined?
Have any environmental factors been associated with the problem in others? If so, how convincingly?
Could the identified hazards cause this problem?
Has the dose been sufficient to result in an illness?
Does the temporal relationship of exposure make sense?
How does an environmental contribution to the problem compare in overall likelihood to other etiologies under consideration?
Rarely will a child health care provider have sufficient data or time, or the expertise, to conclude an environmental medical assessment with certainty. Rather, the data will usually permit only an estimate (≥0.5 or 50% chance) of the likelihood (risk) of a future illness or the probability of a causal connection to an existing disease.
Note: Hill (1965) defined five criteria that should be fulfilled to establish a causal relationship. These five criteria have been generally adopted as a test of causation. The criteria are
consistency of the association (i.e., different studies resulted in the same association);
strength of the association (i.e., size of the relative risk found increased if dose response can be established);
specificity of the association (i.e., measurability of the degree to which one particular exposure produces a specific disease);
temporal relationship of the association (i.e., exposure to the factor must have preceded development of the disease); and
coherence of the association (i.e., biologic plausibility).
Risk estimates can range from negligible (a lifetime excess cancer risk of 1 in 106) to levels of public health concern. In most forensic settings, the expression "more probable than not" (≥0.5 or 50% chance) describes the appropriate standard for decision-making. In most public policy decision-making, environmental agencies aim to reduce risks to negligible levels. Doses relevant to risk assessments are expressed in milligrams/kilograms/day based on age/weight and physiologic differences.
In the exam room, no single probability threshold exists for recommending intervention. The more certain the hazard is as associated with an exposure, the stronger the indication for action. The clinician must consider the probability of adverse effects, as well as what interventions are available and their benefits.
For example: If a child has
acrodynia clearly linked to chronic mercury contamination at home, removal of the child from the home pending remediation of the hazard is mandatory. On the other hand, the negligible risks of future illness from undisturbed, nonfriable
asbestos insulative pipe covering (i.e., lagging to prevent heat loss) in a basement, compared to the high costs and difficulty of safe removal, point to the wisdom of encapsulating and/or leaving the asbestos alone.
On the basis of personal, social, and economic considerations, the risks that families consider acceptable vary. EPA has told the public that radon causes lung cancer, yet only a small percentage of people have measured and remediated radon problems in their homes. The clinician's responsibility is to blend knowledge of the medical significance of environmental exposure with an understanding of the other factors that families consider when deciding to take action.
