The Reliability of Toxicity Standards

You may ask, “Can I trust exposure limits set by our regulatory agencies?”

Assuming that test results are reported without bias or censure – not a certainty in government agencies – the answer depends crucially upon what effects were observed and recorded in the toxicology studies. Did the investigators use only crude measures of effects, such as body weight or the presence of tumors; or were finer measures used, such as the presence of birth defects or hormone disorders; or finer yet, behavioral and learning disorders? Fortunately, more and more toxicological studies are measuring finer unhealthful effects, such as reproductive and developmental defects.

There is inherent difficulty in reaching scientific consensus on the safety or hazard of suspect chemicals, and therefore difficulty in setting a safe standard. Two government-convened panels reached nearly opposite conclusions on the health risks from Bisphenol-A (BPA), used to make polycarbonate plastic bottles and epoxy linings for food cans. Furthermore, standards not infrequently change as more data become available. The original “safe dose” for BPA was 5mg/kg (of body weight/day; as toxic effects began to appear in laboratory animals at this dose,  the “safe dose” was lowered to 0.10 mg/kg/day; further observations of reproductive defects in frogs led to a “safe dose” of only 0.0024mg/kg/day.

Different government agencies can arrive at different limits for exposure to a toxic substance. In the case of cadium (as in nickel-cadium rechargeable batteries), the maximum limit for an adult has varied from 14 micrograms/day by the ATSDR, 20 micrograms/day in water by the FDA, 35 micrograms/day in water by the EPA, and 70 micrograms/day in food by ATSDR and EPA. Confusing!

Different agencies give different rating for the risk of cancer. For example, for cadmium the American Conference of Industrial Hygienists rate it as a suspected carcinogen; EPA rates it a probable human carcinogen; the National Toxicology Program and the International Agency for Research on Cancer both rate it as a known human carcinogen.

Other considerations in judging the risk to health from exposure to a toxic substance are unknowns and uncertainties inherent in risk assessment. Peter Montague has given a good description of assumptions in risk assessment (in the book Ecological Medicine).
1. It is assumed that we can know how much of an activity (e.g., spraying a pesticide) is dangerous or destructive.
2. It is assumed that if there are dangers to this activity, we will learn of them before permanent or major damage has occurred.
3. It is assumed that we are smart enough to go chemical-by-chemical, activity-by-activity, factory-by-factory, river-by-river, ocean-by-ocean, everywhere in the United States, and by extension, everywhere on the planet, and set numerical limits to those activities.

A final consideration arises from the fact that toxicity limits are experimentally determined for exposure to a single toxic chemical, whereas people carry multiple toxic in their bodies. Even if your body’s toxic burden for one specific chemical is only one tenth of the limit set by US agencies, the presence of ten or more similar toxics could push your body’s load above recommended limits. A concluding message might be “minimize the amount of all toxics in your body.”

ATSDR is the Agency for Toxic Substances and Disease Registry. FDA is the Food and Drug Administration. EPA is the Environmental Protection Agency.

 

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About donlouis

The author has long had a keen interest in staying healthy and fit, and in doing whatever I can to keep the natural environment unpolluted and a healthy space for people and all animals. As a former Board Member of a municipal water district, I regularly had to deal with the issue of water quality. I first became aware of radiation hazards from toxic materials while working on uranium for nuclear reactors. During the 1960s I was tuned into the global hazard from Strontium 90 raining down from atmospheric testing of nuclear bombs. While working in the chemical industry in later years I became aware of the many forms of chemical contaminants entering the environment every day, and resolved to do something about it. I am able to make sense out of the voluminous descriptions of common toxic chemical because of my training in chemistry, with a Ph.D. degree and several decades of research and development work in the chemical industry. My training and experience enables me to present to readers reliable and current information on the topic of chemical hazards in the environment, and their threats to human health. All my life I have loved hiking and camping in nature. Skiing, river kayaking, and tennis have been my favorite physical activities. Nature photography is my artistic passion.
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