Human testing: Sass and Needleman respond to industry.

In the March 2004 issue of EHP, we reported on two examples of industry-sponsored studies that intentionally dosed human subjects with toxic pesticides (Sass and Needleman 2004). The four industry-sponsored respondents (Charnley and Patterson 2004; Chart et al. 2004; McAllister 2004; Tobia et al. 2004) focused primarily on their claims that the studies were conducted in accordance with formal ethical guidelines. Although that contention is debatable, it misses fundamental scientific criticisms we raised: a) sample sizes and statistical power were too small to find an effect, if one were present; b) study populations were inappropriate to establish no observed effect levels (NOELs) for children, the most sensitive population; c) outcome measures were unsuitable to establish NOELs for children; and d) study interpretations were biased to ignore or dismiss evidence of adverse health effects. The pesticides under consideration were organophosphate neurotoxins that are chemically related to military nerve gas.

We would like to respond to Charnley and Patterson (2004), Chart et al. (2004), McAllister (2004), and Tobia et al. (2004) in detail.

First, if there is no chance of obtaining valid conclusions, one cannot ethically expose humans to risks. A recent National Research Council (NRC) report (NRC 2004) stated that underpowered studies "cannot be ethically acceptable if [they are] scientifically invalid." The industry human experimentation studies conducted to date employed samples of < 60 subjects (AMVAC 1997; Haines 1971; Wyld et al. 1992). The calculated statistical power to find an effect was in the range of 0.2. This means that they had a one-in-five chance of detecting an effect if it were present, practically guaranteeing a finding of no effect.

Second, the outcome measures in the industry studies were peripheral red blood cell acetyl cholinesterase (AChE) levels, a symptom checklist, and blood pressure (AMVAC 1997; Haines 1971; Wyld et al. 1992). The insensitivity of these measures stands in contrast with recent literature on low-dose noncholinergic toxic effects of the organophosphate pesticides (OPs), including effects on neurogenesis and behavior (Aldridge et al. 2004; Icenogle et al. 2004; Meyer et al. 2004a, 2004b). Although the primary outcome of interest in protecting children is the effect of OPs on the developing brain, neurobehavioral toxicity was not evaluated in any of the industry reports (AMVAC 1997; Haines 1971; Wyld et al. 1992). In addition, whereas evidence of carcinogenic properties has been published on a number of OP pesticides, no attempt has been made to evaluate this or any other chronic end point.

Third, there was no urgent or compelling need for human data, given the existing evidence of toxicity from laboratory experiments. Industry sought information from human studies primarily to avoid the 10-fold safety factor when extrapolating from animal studies to human risk. Eliminating the safety factor would result in setting higher levels of allowable exposure and permit greater sales of the pesticides.

Fourth, the AMVAC Chemical Corporation, sponsor of the dichlorvos (DDVP) study we discussed (AMVAC 1997), reported that although there were statistically significant differences in cholinesterase inhibition between treated and placebo groups, "none of these differences were considered to be of biological significance," and the dose was considered a NOEL. However, the U.S. Environmental Protection Agency (EPA) rejected AMVAC's interpretation of the results, instead concluding that "the reduction in RBC cholinesterase activity was considered by the Hazard ID [identification] Committee to be biologically significant," and the dose tested was considered to be a lowest observed effect level (LOEL) (U.S. EPA 1998b). This illustrates our concern that, "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" (Sass and Needleman, 2004).

The responders from Bayer CropScience (Tobia et al. 2004) stated that in our letter we omitted the critical fact that the Bayer-sponsored aldicarb study on human subjects had been reviewed and found "acceptable and appropriate" by a U.S. EPA Scientific Advisory Panel (SAP) in 1992 and reaffirmed in 1998. In 1992 the SAP had no ethical guidelines governing acceptance of human studies. As to the 1998 review, the statement by Tobia et al. (2004) is misleading. In fact, the U.S. EPA statement issued in 1998 to the SAP/Science Advisory Board (SAB) (U.S. EPA 1998a) reads in its entirety:

   [The U.S.] EPA is deeply concerned that some
   pesticide manufacturers seem to be engaging in
   health-effects studies on human subjects as a way
   to avoid more protective results from animal tests
   under the new Food Quality Protection Act. The
   government has in place very stringent standards
   that apply to federally funded research to ensure
   the protection of human subjects. [The U.S.]
   EPA will be asking its independent Science
   Advisor, Board to apply these same standards to
   pesticide data submitted to [The U.S.] EPA by
   companies for review. No human test data [have]
   been used by [The U.S.] EPA for any final decisions
   about acceptable levels of pesticide under
   the new food safety law. The protection of public
   health from adverse effects of pesticides can be
   achieved through reliance on animal testing and
   use of the highest ethical standards.

The U.S. EPA SAP/SAB members were in strong agreement that neurotoxic agents should be given to humans only if there was an urgent and compelling need for the information, and if there was no other way to obtain it (U.S. EPA 2000).

There is growing literature on noncholinergic effects of organophosphates. Meyer et al. (2004a) recently reported developmental alterations in adenylyl cyclase signaling in rat pups exposed to chlorpyrifos, confirming neurodevelopmental effects through noncholinergic mechanisms. Icenogle et al. (2004) reported behavioral changes in adolescent and adult rats after low-dose chlorpyrifos administration. In humans, Berkowitz et al. (2004) reported a small but significant reduction in head circumference in infants born to mothers with detectable levels of chlorpyrifos in their blood, coupled with low maternal paraoxonase (PON1) activity. Perera et al. (2003) reported that chorpyrifos and diazinon found in mother's blood and umbilical cord blood was associated with lower infant birth weight and length, suggesting poorer predicted health outcomes. In an update, Whyatt et al. (2004) reported that regulatory restrictions on the two pesticides measurably lowered exposure and resulted in increased infant head size, providing encouragement for strict regulations to prevent or limit exposure.

The regulation of pesticides must protect against neurodevelopmental and neurobehavioral effects from even low-dose exposures during critical stages in fetal and neonatal development. Measures of cholinesterase in adult peripheral blood are a poor surrogate for these critical effects. The examples of industry-sponsored human tests of pesticides are indefensible on both the scientific and ethical grounds, and U.S. EPA acceptance of such data for setting standards opens the door to serious harm to the general public as well as the subjects of such tests.

The authors declare they have no competing financial interests.

REFERENCES

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Jennifer B. Sass

Natural Resources Defense Council

Washington, DC

E-mail: [e-mail]

Herbert L. Needleman

University of Pittsburgh School of Medicine

Pittsburgh, Pennsylvania

E-mail: [e-mail]