Decade of the Brain
The brain of humans distinguishes
Homo sapiens
from all other animals, yet it remains the least understood of all organs in the body. There has been a curious dichotomy in the evolution of the brain. This vital organ is protected from physical damage by the skull and from selected agents by the blood-brain barrier, yet it lacks the capacity for cell regeneration and is dependent on aerobic metabolism for cellular energy. The vulnerability of the brain to chemical insult is outlined in the first
Focus article
(p. 920). Hundreds of chemicals are known to cause neurotoxicity, and thousands more are suspected. The specificity of chemical damage to the brain is being exploited by neurobiologists and neurotoxicologists in collaborative studies of function and toxicity. The Decade of the Brain emphasizes that understanding, prevention, and treatment of brain disease can best be accomplished in coordinated studies by many relevant scientific disciplines.
Noise + Chemicals = Deafness
The fact that 28-34 million Americans suffer deafness or hearing disorders and that half the people over 75 live with hearing impairments emphasizes the importance of this special sense. Most hearing loss is preventable by avoiding exposure to physical sources like loud noises and exposure to numerous chemicals that can permanently destroy specialized cells for reception and modulation of sound
(p. 924)
. Many organic solvents, drugs, and heavy metals can cause deleterious effects on hearing. Current research is focused on understanding the molecular biology of the auditory process in the hope of uncovering ways to prevent or reverse hearing disorders.
Incinerator Emissions
Incinerators licensed for hazardous waste disposal are required by EPA to undergo a trial burn to determine their performance characteristics. The limitations of this procedure are apparent because emissions are dependent on physical and biological parameters that are unpredictable and incompletely understood. With support from NIEHS, UC-Berkeley and MIT developed technology to monitor emissions in real time. This month's
Innovations
article (p. 932) discusses these prototypes.
Ecosystem Toxicity
"Ecosystem services" include all the processes in nature necessary for the provision of food and potable water, decomposition of sewage, and replenishment of fresh air. Damage to the environment resulting in loss of these services underscores the risk of toxicants to the public. However, to be recognized the damage must be intense, local, and immediate, whereas global changes are difficult to measure and poorly understood. Cairns and Niederlehner
(p. 936)
discuss the utility of models that can extrapolate between these extremes to improve risk assessment procedures.
Aluminum Toxicokinetics
DeVoto and Yokel
(p. 940)
review aluminum toxicokinetics in mammals with special reference to gastrointestinal absorption and speciation in plasma. Exposure to aluminum occurs via food, drinking water, and pharmaceuticals, as well as by inhalation in the workplace. Aluminum absorption is dependent on pH, and 80-90% is bound to the iron transport protein transferritin in plasma. Models suggest that the remainder of the charged species is unavailable for tissue uptake.
3-D PBTK Visual Model
A physiologically based toxicokinetic model was developed using rainbow trout. Nichols et al.
(p. 952)
used magnetic resonance imaging to produce a computer generated three-dimensional image of the fish. Five tissue volumes corresponding to liver, kidney, muscle, gastrointestinal tract, and fat were produced. Models of kinetic data for the disposition of pentachloroethane were mapped onto corresponding tissue volumes, with color intensity representing chemical concentration. Images could then be animated to illustrate accumulation of chemical in each tissue during continuous exposure via the gills.
Copper in Drinking Water
Five cases of elevated copper in drinking water were reported in Wisconsin. Knobeloch et al.
(p. 958)
suggested that water containing above 1.3 mg/l copper may cause diarrhea, abdominal cramps, and nausea, particularly in infants and young children. The blue-colored, copper-contaminated water came from a variety of sources, including shallow wells and unconditioned water pipes or new copper plumbing. As with other metal contaminants in water sources, running the water a short time before use reduced the exposure to acceptable levels.
Dioxins in the Supermarket
Schecter et al.
(p. 962)
analyzed 18 dairy, meat, and fish samples from a New York supermarket to estimate intake of dioxins. Toxic equivalents of TCDD ranged from 0.04 to 0.7 parts per trillion in dairy products, from 0.03 to 1.5 in meat, and from 0.02 to 0.13 in fish. Based on average 1986 food consumption data, an adult would ingest 0.3-3.0 pg/kg body weight of the toxic equivalents of TCDD daily, whereas nursing infants might consume 35-53 units during their first year. These levels are markedly higher than the EPA virtually safe dose of 0.006 units of TCDD over 70 years. A vegetarian diet would result in reduction of toxic equivalents of TCDD to between 0.006 and 0.06 units.
Dioxins in Human Milk
Dioxin concentrations in milk were not influenced by varying the fat content of the diet during breast-feeding. Pluim et al.
(p. 968)
compared diets with 20% energy from fat to those with 50% energy from fat. The authors conclude that the only way to reduce the dioxin concentration in breast milk is lifelong reduction of fat consumption, since dioxin is ubiquitous in the environment and is concentrated in animal fats.
Oxidants and Bronchial Cells
Gabrielson et al.
(p. 972)
compared cytotoxic and genotoxic effects of hydrogen peroxide and ozone on cultured human airway epithelial cells. Both compounds inhibited the replicative ability of epithelial cells and at high doses caused acute cytotoxicity. The effects of ozone were not mediated through peroxides or DNA breaks, indicating that other reactive species are responsible for ozone toxicity.
Last Update: June 18, 1998
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