Industry testing of toxic pesticides on human subjects concluded "no effect," despite the evidence.
DDVP, an organophosphate pesticide, exerts its toxicity through inhibition of acetyl cholinesterase. Symptoms of poisoning include diarrhea, vomiting, salivation, convulsions, and--in extreme cases--death. DDVP is widely used in pesticide-impregnated resin strips. It is listed as a possible human carcinogen by the International Agency for Research on Cancer (IARC 1991) and a probable human carcinogen by the U.S. EPA (1994). The AMVAC Chemical Corporation submitted a report to the U.S. EPA titled Dichlorvos: A Single Blind, Placebo Controlled, Randomized Study to Investigate the Effects of Multiple Oral Dosing on Erythrocyte Cholinesterase Inhibition in Healthy Male Volunteers (AMVAC 1997). According to the report, subjects were given 21 daily oral doses of 7 mg dichlorvos (six subjects), or placebo (three subjects). A venous blood sample was taken every 2-3 days, immediately before dosing. The authors (AMVAC 1997) reported that, compared with the group mean predose cholinesterase activity,
The repeated measures analysis of variance [ANOVA] showed statistically significant differences from the placebo group (1% level) on days 7, 11, 14, 16, and 18.
Despite these reported effects, the study concluded that "none of these differences were considered to be of biological significance" and that "a no observed effect level was established at 7 mg dichlorvos (equivalent to approximately 0.1 mg/kg/day for a 70 kg male) ..." (AMVAC 1997). The conclusion attempted to dismiss the measured effects on cholinesterase inhibition by the poorly substantiated assertion that no relevant biological consequences would be expected at this level of inhibition, whereas the only biological end point measured in the study was cholinesterase inhibition, and this was significantly inhibited.
Aldicarb, a carbamate pesticide, also exerts its toxicity through acetyl cholinesterase inhibition. Allowable levels of aldicarb on food were set by the U.S. EPA in 1977, based on data from an unpublished report by Union Carbide (Haines 1971). Union Carbide tested three groups of four healthy adult males (at 0.025, 0.05, and 0.1 mg aldicarb per kilogram body weight, with no placebo of control group), and determined that, on the basis of subclinical blood cholinesterase inhibition, 0.025 mg/kg aldicarb was the lowest dose having an effect (lowest observed effect level; LOEL). From this study the U.S. EPA set a no observed effect level (NOEL; the maximum dose having no effect) for cholinesterase inhibition of 0.01 mg/kg/day (National Research Council 1997) (Figure 1). Subsequent food poisoning incidents, however, demonstrate the danger of reliance on such studies. In 1990, Goldman et al. (1990) published a report of three aldicarb food-poisoning incidents. The LOEL was 0.0023 mg/kg, observed in a 66-year-old woman after she consumed contaminated cucumber (Figure 1). Goldman et al. (1990) reported that "within 45 minutes she experienced nausea, vomiting, sweating, dizziness, loss of balance, disorientation, and fatigue." Most estimated dosages resulting in adverse effects were well below the 0.025 mg/kg LOEL reported by Union Carbide (see study comparison in Figure 1).
[FIGURE 1 OMITTED]
Following the food-poisoning incident, Rhone-Poulenc (Lyon, France) took over the registration of aldicarb. It then sponsored a single oral dose, double-blind placebo-controlled study with human subjects (Wyld et al. 1992) using the following doses: placebo (16 males, 6 females), 0.01 mg/kg (8 males), 0.025 mg/kg (8 males, 4 females), 0.05 mg/kg (8 males, 4 females), and 0.075 mg/kg (4 males). Wyld et al. (1992) reported that red blood cell cholinesterase activity was statistically significantly depressed at all doses compared with the placebo group (repeated measures ANOVA, two-tailed, 5% significance level). Despite a total of 24 adverse events reported by subjects (localized sweating, lightheadedness, headache, salivation), the authors reported that only one event was treatment related (profuse sweating in the highest dose group). Wyld et al. (1992) reported that there were no treatment-related clinical symptoms at doses [less than or equal to] 0.05 mg/kg (the study NOEL), a dose that was severe enough to require hospitalization and atropine treatment for one person in the California food-poisoning incident (Goldman et al. 1990).
A study of a handful of healthy adult subjects is inadequate to determine the expected response to toxic chemical exposures from population diverse in ethnicity, life-stage, sex, health status, genetic makeup, metabolism, and nutritional status. Such studies often lack enough subjects to provide adequate statistical power to detect an effect if it is present (Bekelman et al. 2003). When studies are sponsored by chemical manufacturers with a financial interest in the study outcome, the studies may be biased in design and in interpretation. Efforts by the chemical manufacturers to foist these scientifically misleading studies on the U.S. EPA in order to weaken regulatory standards is profoundly troubling.
The authors declare they have no competing financial interests.
AMVAC. 1997. Dichlorvos: A Single Blind, Placebo Controlled, Randomized Study to Investigate the Effects of Multiple Oral Dosing on Erythrocyte Cholinesterase Inhibition in Healthy Male Volunteers. Report No CTL/P/5392. Study No. XH6063. MRID No. 442405-01. Newport Beach, CA:AMVAC Chemical Corporation.
Bekelman JE, Li Y, Gross CP. 2003. Scope and impact of financial conflicts of interest in biomedical research: a systematic review. JAMA 289:454-465.
Goldman LR, Beller M, Jackson RJ. 1990. Aldicarb food poisonings in California, 1985-1988: toxicity estimates for humans. Arch Environ Health 45:141-147.
Haines RG. 1971. Ingestion of Aldicarb by Human Volunteers: A Controlled Study of the Effect of Aldicarb on Man. Union Carbide Corporation Study No. ALD-03-77-2215. MRID No. 00101911. HED Doc. Nos. 007601, 010450. Washington, DC:U.S. Environmental Protection Agency.
IARC. 1991. Dichlorvos. IARC Monogr Eval Carcinog Risks Hum 53:267-307.
Mitka M. 2003. EPA ponders pesticide toxicity testing: considers ending moratorium on human data, JAMA 289(5):535-536.
NAS. 2003. Use of Third Party Toxicity Research with Human Research Participants. Project No. STLP-Q-02-02-A. Washington, DC:National Academy of Sciences. Available: http://www4.nas.edu/webcr.nsf/MeetingDisplay4/STLP-Q-02-02-A?OpenDocument [accessed 11 February 2004].
National Research Council. 1977. Drinking Water and Health. Washington, DC:National Academy of Sciences. Available: http://www.nap.edu/books/0309026199/html/index.html [accessed 11 February 2004].
U.S. EPA. 1994. Integrated Risk Information System: Dichlorvos (CASRN 62-73-7). Washington, DC:U.S. Environmental Protection Agency. Available: http://www.epa.gov/iris/subst/0151.htm [accessed 9 February 2004].
Wyld PJ, Watson CE, Nimmo WS, Watson N. 1992. A Safety and Tolerability Study of Aldicarb at Various Dose Levels in Healthy Male and Female Volunteers. Rhone-Poulenc, Lyon, France. Inveresk Clinical Research Report No. 7786. MRID No. 42373-01. HED Doc No 010459. Washington, DC:U.S. Environmental Protection Agency.
Jennifer B. Sass
Natural Resources Defense Council
Herbert L. Needleman
University of Pittsburgh School of Medicine
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|Author:||Needleman, Herbert L.|
|Publication:||Environmental Health Perspectives|
|Date:||Mar 1, 2004|
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