Essay: Chlorpyrifos

ABSTRACT: Chlorpyrifos is an effective organophosphate insecticide that is widely popular in the U.S. agricultural sector. It is also an effective neurotoxicant and developmental toxicant, that has been associated with stunted growth and impaired cognitive function. The U.S. Environmental Protection Agency ordered that the pesticide be phased out from most household uses in 2000 because of evidence that exposures in U.S. households were expected to cause unacceptable levels of harm. Despite pressure from scientists and advocacy groups, chlorpyrifos is not banned for agricultural uses in the U.S even though the EPA has proposed doing so. This paper explores the history of chlorpyrifos regulation, the health effects of chlorpyrifos exposure, and the influences from industry and politics that have led to the recent revocation of a proposed ban. This paper concludes with a discussion of the policy changes that could improve the process for regulating and enforcing pesticide use and exposure.
1. Introduction
Pesticides are important substances for the nation’s agricultural system as they improve crop yield and reduce production costs through the control of pests and weeds, but they can be potentially harmful to human health because of their inherent purpose to harm or kill plants and animals. The U.S. Environmental Protection Agency (EPA) has the authority to regulate pesticide production and use in this country, but critics have argued that this authority is not always used to the fullest extent to protect the public’s health. Politics, scientific uncertainty, and industry influences have played a role in slowing regulatory decision making with regards to pesticides known to be hazardous to human health. One example of this is the pesticide chlorpyrifos. Chlorpyrifos, a widely-used insecticide that has been shown to cause a wide range of adverse effects in humans, is not banned in the U.S. despite a proposal to do so because of political influences, pressure from the manufacturer, scientific uncertainty, and limitations in the laws governing pesticide regulations.
2. Background
a. Chlorpyrifos
Pesticides are categorized by the types of pests they are formulated to kill, with herbicides and insecticides being the most commonly used domestically and internationally.1 For populations working in the agriculture sector or living near fields where pesticides are applied, common routes of pesticide exposure are accidental ingestion, inhalation, and dermal absorption. Other routes of exposure are inhalation, ingestion, or dermal absorption of pesticides applied inside homes or gardens in attempts to eliminate domestic pests. Individuals can also be exposed to pesticides by consuming produce and food products that contain pesticide residues.
Chlorpyrifos is an organophosphate insecticide and the most commonly used insecticide in the U.S. agricultural sector, according to the most recent statistics.1 In 2012, it was estimated that between five and eight million pounds of chlorpyrifos were used in the U.S.1 It is used on a wide variety of crops, including wheat, cotton, alfalfa corn, soybeans, almonds, apples, asparagus, peppers, peaches, onions, peas, grapes, cherries, strawberries, citrus fruit, and broccoli.2 It was first produced in 1965 by Dow Chemical Company and is commonly sold under different product names, such as Dursban and Lorsban. Chlorpyrifos became a popular alternative to dichlorodiphenyltrichloroethane (DDT), an insecticide banned in 1972. (DDT was as substitute for arsenic-containing pesticides, like lead arsenate.)3
Chlorpyrifos is quickly metabolized and excreted in humans, so it does not accumulate to a significant level. Its half-life in the body has been estimated to be between 15-30 hours.4,5 The half-life of chlorpyrifos in soil is much longer, on the order of months.6 Researchers have shown that chlorpyrifos exposure in the homes of pesticide applicators and homes near fields where pesticides are applied is common.7 The United States Geological Survey reported that between 1992 and 2001, chlorpyrifos was frequently (approximately 30% of samples) detected in urban streams, as well as steams on agricultural and mixed use land.6 The high frequency of detection in urban streams can be explained by the popularity of chlorpyrifos-containing insecticide products used in households and gardens during this time period, about 5 million pounds per year.6 California, North Dakota, Minnesota, Iowa, and Texas are the states where the most chlorpyrifos is applied, in terms of pounds.2
Accidental poisonings are an important exposure pathway, especially for young children whose parents or guardians may keep pesticide-containing products in the house. In 1999, there were 11,193 organophosphate exposure cases reported to Poison Control Centers in the U.S. Of these, 3,420 (31%) were among children less than six years old.8
While there have been numerous studies examining the health effects of chlorpyrifos exposure, there are three major cohort studies that have been instrumental for the arguments in support of a chlorpyrifos ban. Dr. Virginia Rauh and other researchers at Columbia University’ Center for Children’s Environmental Health lead a study 725 mothers and their children in New York City that measured chlorpyrifos exposure and long-term neurological outcomes. In one highly-cited paper from this cohort data, the researchers examined the association between prenatal chlorpyrifos exposure (measured as chlorpyrifos concentration in umbilical cord blood) and cognitive and motor development at one-year intervals from years one to three. They found that children with higher prenatal chlorpyrifos exposure (>6.17 pg/g plasma) scored lower on the motor development and mental development tests than those with lower exposure levels, even after controlling for important covariates like maternal IQ, maternal education, and sex. They also found significant associations between chlorpyrifos exposure and attention problems and attention-deficit/hyperactivity disorder (ADHD) incidence.9 In a follow-up study, these researchers looked at similar outcomes for the same children at age seven. They found that for every standard deviation increase in prenatal chlorpyrifos exposure, there was a 1.4% decrease in IQ and 2.8% decline in working memory, after controlling for the same covariate as before.10
Another cohort examining the relationship between pesticide exposure and health outcomes in children is the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) cohort in California led by researchers at University of California, Berkeley. This was a birth cohort of children whose parents lived and worked in the farms of Salinas Valley, California. Their studies relied on surrogates of organophosphate exposure, such as 3,5,6-trichloro-2-pyridinol (TCPy), dialkyl phosphate (DAP), paraoxonase 1 (PON1). Chlorpyrifos was being applied in fields within the study region so exposure was expected, as was exposure to other organophosphates. They found that increased DAP levels (surrogate for exposure to multiple organophosphates) was significantly associated with declining scores on the mental development index.11
Finally, researchers at Mount Sinai School of Medicine conducted a longitudinal birth cohort in New York City of more than 400 pregnant women recruited between 1998 to 2002. They measured organophosphate metabolites in maternal urine during pregnancy and followed the children for 9 years to determine any potential effects of neurodevelopment and behavior. These researchers found similar results as those reported by the University of California, Berkeley team. Increased DAP levels (surrogate for organophosphate exposure) were associated with mental development decrements, like declines in perceptual reasoning, in children at 12 months, particularly among those children whose mothers were genetically more susceptible to organophosphate toxicity.12
There is toxicological evidence that chlorpyrifos can also cause harm to other organs, such as the kidneys. Experimental studies in rats exposed to chlorpyrifos demonstrated structural and histopathological changes in the kidneys, including tubular swelling, shrunken glomeruli, tubular dilation, hypertrophy of tubular epithelial cells, degenerated tubules, and tubular vacuolization 13,14, as well as functional changes observed as increases in blood urea nitrogen and serum creatinine. 15 Histopathological changes have also been observed in fish following chlorpyrifos exposure. 16–18 In a study in mice, in utero exposure to chlorpyrifos led to decreased kidney weights in female offspring and increased kidney weights in male offspring. 19
Researchers have also found evidence of kidney damage and disease following exposure to organophosphate pesticides in humans. A cohort study in Taiwan found that patients with organophosphate poisoning had six times the risk of developing acute kidney injury compared to controls 20. In a cross-sectional study in El Salvador, researchers found that methyl parathion contact was significantly associated with chronic kidney disease prevalence. 21 In a cross-sectional study in India, serum creatinine levels were significantly higher in a group of occupational workers exposed to a mixture of chlorpyrifos, temephos, malathion, and pirimiphos methyl when compared to a control group. 22
Organophosphate pesticides, including chlorpyrifos as well as diazinon, malathion, and parathion, are effective insecticides because they inhibit acetylcholinesterase in nerve cells. Acetylcholinesterase is an enzyme that breaks down acetylcholine following a neurotransmission. When acetylcholinesterase is inhibited, acetylcholine is not broken down, and the pathway for neurotransmission is impaired.23 Acetylcholinesterase inhibitors, like organophosphates, are known toxicants with manifestations that include bradycardia, seizures, salivation, paralysis, dizziness, nausea, vomiting, confusion, respiratory paralysis, and death.24
Organophosphates are so effective that they have been used as chemical weapons, which include widely known substances like sarin and tabun. A German scientist, Gerhard Schrader, developed tabun in 1936 in an attempt to create an effective insecticide. However, he discovered that it was very toxic to humans, causing vomiting, drooling, diarrhea, and death. The German army realized that tabun was a much more effective than chemical weapons they had been using (like mustard gas and phosgene) because it only took 20 minutes to kill its victims. Two years later, Schrader invented sarin, an even more toxic nerve agent than tabun.25 In March 1995, domestic terrorists used sarin to kill 12 people and injure thousands more on five crowded Tokyo subway trains during morning rush hour. Survivors reported symptoms ranging from headaches and fatigue to vision problems and depression.26
Fortunately, the use of organophosphate pesticides in the U.S. has decreased rapidly since 2000. As a percentage of total insecticides, organophosphate use has decreased from 71% to 33% between 2000 and 2012.1 These have been largely replaced by the use of other types of insecticides, like pyrethroids and neonicotinoids. Chlorpyrifos was phased out of consumer pesticide products in 200027, but interestingly, the geometric mean of creatinine-corrected TCPy (a primary metabolite of chlorpyrifos) increased in the general population from 1999/2000 to 2001/2002, according to the National Health and Nutrition Examination Survey (NHANES), a representative biomonitoring survey. This increase was observed among all age groups, including 6-11 year olds, and more pronounced among Mexican Americans, who had the highest mean exposure in 2001-2002 amongst all of the reported racial and ethnic categories. The highest overall exposure levels were observed among 6-11 year olds, for both time periods.28
In July 2016, a group of public health researchers and health professionals issued a statement calling for more research on and reductions in exposures to environmental neurotoxicants. In this statement, they specifically mention organophosphate pesticides as one of a few “prime examples of neurodevelopmentally toxic chemicals” and cite the research conducted at Columbia University and University of California, Berkeley for this claim.29 Linda Birnbaum, the director of the National Institute for Environmental Health Sciences, was a co-author on this statement.
Despite the general consensus from the scientific community, representatives from Dow Chemical Company, a major manufacturer of chlorpyrifos, have consistently disputed the adverse health effects found to be associated with chlorpyrifos exposure and claim that the chemical is safe for humans to use. On their website, chlorpyrifos.com, Dow disputes the findings of the Columbia and Berkeley researchers, stating: “Inherent issues with study design and exposure assessment limit the confidence that can be placed on the findings of these studies. The weight of the evidence continues to demonstrate that chlorpyrifos does not cause developmental effects.”30
Dow has even released a white paper describing in detail the limitations of the research conducted at Columbia on chlorpyrifos and neurodevelopmental outcomes.31 They argue that this research is inconsistent with other studies on the topic, reports low exposure levels, includes only one measure of exposure, and may have internal validity issues. They also argue that while the researchers at Columbia found significant associations between chlorpyrifos exposure and impaired neurodevelopment, intelligence, and behavior, the other two cohort studies only found significant associations for DAP levels, and no associations for the chlorpyrifos-specific biomarkers DEP and TCPy. The exception is full-scale IQ score, for which both Columbia and Berkeley researchers found significant decreases in IQ with chlorpyrifos exposure (measured as DEP in the Berkeley research). Dow also criticized research by the same team at Columbia looking at differences in brain scans of children highly exposed to chlorpyrifos compared to children with low exposure.32
However, Dow’s own research has been called into question by scientists. A lawyer in the early 1990s contacted a Stanford neuroendocrinologist, Robert Sapolsky, to serve as an expert witness in a case of chlorpyrifos poisoning in which a family was suing Dow. As part of his role in this case, Dr. Sapolsky reviewed internal Dow reports and published papers by Dow scientists on the health effects of chlorpyrifos exposure. In a white paper33, Sapolsky describes the conclusions he and several Stanford post-doctoral fellows came to upon reviewing these documents. They report that the majority of these papers and reports suffer from substantial flaws in methodology, design, interpretation, and analysis. They also noted that errors found in these papers consistently led to findings that chlorpyrifos exposure was safe for humans, and none led to findings of the contrary.
b. Pesticide Regulation in the United States
The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) (7 U.S.C. §§ 136 et seq.) is the law that governs pesticides in the United States. Congress originally wrote the law to give the United States Department of Agriculture (USDA) the authority to regulate claims of pesticide efficacy made by pesticide manufacturers in an attempt to give farmers more information about the pesticides they were purchasing.34 In 1972, the Federal Environmental Pesticide Control Act (7 U.S.C. §§ 136-136y), transferred the authority to the newly-formed EPA and gave the agency the responsibility for overseeing the sale and use of pesticides through a registration-based system.35 FIFRA outlaws the sale or distribution of pesticides that are not registered by EPA or pesticides with canceled registrations.
The EPA Office of Pesticide Programs considers the safety of a pesticide when reviewing it for registration. The burden of proof is on the manufacturer to prove that the pesticide will not “cause unreasonable adverse effects on the environment” when applied as directed. Unreasonable adverse effects in this case are defined as: “(1) any unreasonable risk to man or the environment, taking into account the economic, social, and environmental costs and benefits of the use of any pesticide, or (2) a human dietary risk from residues that result from a use of a pesticide in or on any food” in accordance with the Federal Food, Drug, and Cosmetic Act (described below).36 EPA re-reviews pesticides every fifteen years or less (called reregistration) to consider additional evidence regarding a pesticide’s eligibility for FIFRA registration. They are currently reviewing 725 registrations, which in total cover over 1,100 active ingredients.37 When EPA conducts a registration or re-registration review, they conduct a risk assessment, which are publicly available documents that the public is able to provide comment on.37
In addition to the review of pesticides before registration, EPA requires that each pesticide has the appropriate labeling and packaging. Labels on pesticides must include a long list of information about the product, such as the name of the manufacturer, the registration number, the ingredient list, any warnings or precautions, and directions for using the product. Sometimes these labels include information about necessary protective clothing for users and guidance on how much time is needed between application and when workers can re-enter a field.34 EPA requires that packaging for most consumer pesticide products be child-resistant and have the word “danger” or “warning” printed clearly. Under the Worker Protection Standards (40 CFR Part 170), EPA has the authority to require that workplaces that use or handle pesticides enforce workplace standards that reduce pesticide exposures.34 In addition to ensuring safe workplace practices, EPA considers worker safety and health when considering the safety of pesticides. EPA can classify certain pesticides as “restricted use.” For these pesticides, only certified applicators are allowed to use them. EPA established the standards of becoming a certified applicator, but certain states can establish certifying programs of their own, upon EPA approval.34 For chlorpyrifos, EPA requires that workers handling the insecticide wear chemical resistant gloves, coveralls, and respirators. EPA also requires that access to fields where chlorpyrifos has been applied be restricted for 1-5 days.38
Pesticide manufacturers who have pesticides registered with EPA are required to report any incidents of unreasonable adverse effects of the pesticide to EPA, as described in section 6(a)(2) of FIFRA. This information can consist of new data acquired through research (such as toxicity data) or reports of any cases of adverse outcomes following exposure to the pesticide. The information reported to EPA through this mechanism is considered when evaluating pesticides for safety.39
In 1938, Congress passed the Federal Food, Drug, and Cosmetic Act (FFDCA) (21 U.S.C. §§ 301 et seq.) with the intention of protecting consumers from potential hazards in food, drugs, and cosmetics, including from pesticide residues in food. The EPA sets maximum allowable levels called tolerances for pesticide residues in food, under the authority of the FFDCA, while the Food and Drug Administration (FDA) enforces these tolerances on food products made in the U.S. and imported from outside the country, excluding those products that fall within jurisdiction of the USDA, including meat and poultry. A pesticide cannot be applied to a food if there is no tolerance or tolerance exemption by the EPA. The USDA, through the Agricultural Marketing Service (AMS), monitors pesticide residue levels in food products. This authority is granted by the Food Quality Protection Act (FQPA) of 1996 (110 Stat. 1489). EPA uses the data collected by AMS to determine if exposure levels to pesticide residues do not pose unreasonable risk to the public.40
According to published AMS data, the number of instances in which measured chlorpyrifos residue on food products exceeded set EPA tolerances has increased since 2001. This is in large part due to the fact that many foods didn’t have tolerances for chlorpyrifos before this date. Between 2001 and 2010, there were multiple instances of chlorpyrifos residue in exceedance of the limit per year, with peaches, cucumbers, plums, and cilantro being the most common food products with violations. There were two instances of violations recorded in 1996 and 1999 each.41 Chlorpyrifos tolerances have been updated in 2000 (65 FR 33711), 2002 (67 FR 49617), 2006 (71 FR 74817), 2008 (73 FR 53739), and 2011 (76 FR 56656). EPA most recently updated the tolerances for chlorpyrifos residue in 2011, listing tolerance levels for 81 commodities, including alfalfa, apples, corn, eggs, peanuts, peppers, peaches, wheat, and leafy green vegetables. Two foods, asparagus and grapes, have tolerances with regional registrations.42
Pesticides are considered “banned” when EPA does not approve a pesticide for any registered uses or cancels an existing registration (under the authority of section 6(b) of FIFRA). EPA revokes tolerances for pesticide residues when a pesticide is banned, when tolerances are no longer necessary, or when EPA determines a current tolerance does not meet safety standards. EPA can address health and safety concerns by adjusting or canceling a registration and its associated tolerance. Tolerances are automatically revoked when a pesticide registration is cancelled, but still undergo the process of a proposed rulemaking, public comment period, and final rulemaking.43 Pesticide manufacturers are also allowed to voluntarily cancel registrations.
To revoke a tolerance, EPA must publish a proposal in the Federal Register, provide a 60-day comment period for the public (can be shorter with justification), and publish a final regulation in the Federal Register. Members of the public or industry are allowed to submit objections within 60 days of this publishing if they wish to have a judicial review of the rule. EPA must respond to any objections submitted, if there is no hearing. If there is a hearing based on the objections raised, an administrative law judge issues a decision, which can be appealed to either the EPA Administrator or the Environmental Appeals Board (EAB). In the case of an appeal, the decision made by the EAB or Administrator is the final determination, and cannot be further appealed.43
To cancel a pesticide registration, EPA must first conduct a risk assessment and evaluate the benefits of the pesticide. If EPA determines residues of a specific pesticide in food or water exceed the standard of “reasonable certainty of no harm” (section 408 of FFDCA) posed to consumers, it can cancel the pesticide registration based on dietary risks. However, EPA can also cancel a pesticide registration based on risks to residents, farmworkers, or ecosystems. In this scenario, EPA must weigh the benefits associated with the pesticide use when evaluating the risks posed to humans and/or the environment. EPA typically allows for public input before cancelling a pesticide registration, but this is not required by law.44
EPA has banned or restricted certain pesticides in the U.S. through cancelling registrations or denying registration requests. One such pesticide was carbofuran, a carbamate insecticide. In 2007, EPA determined that carbofuran posed both dietary and non-dietary (worker and ecological) risks, so they revoked the tolerances and gave the registrants the opportunity to voluntarily cancel the registrations for carbofuran.45 While some uses were voluntarily cancelled (effective on March 2009), EPA had to use its authority under section 6(b) of FIFRA to cancel the remaining registered uses.46 In July 2010, EPA and the manufacturers of endosulfan came to an agreement to phase out all uses of endosulfan, an organochlorine insecticide, because of the risk its use posed to farmworkers and wildlife. This was considered a voluntary cancellation. The phase-out stated in 2012 and lasted until July 2016, when all uses were no longer lawful.47 In 2000, EPA came to a similar agreement with the registrants of ethyl parathion, an organophosphate insecticide like chlorpyrifos, to cancel all registrations of the pesticide by October 2003.48
3. Legal and Regulatory History of Chlorpyrifos
There is a long legal history of individuals and families suing Dow for reported adverse health effects caused by exposure to chlorpyrifos. In 1990, Vicki and Glen Herb sued Dow Chemical Company over a suspected chlorpyrifos poisoning that severely paralyzed their infant son, Joshua. The Herbs’ lawyer, Stuart Calwell, hired researchers at Duke University, who confirmed pesticide poisoning.49 As part of the discovery process of the case, Calwell requested from Dow any reports of adverse events related to chlorpyrifos exposure that the company was required to report to EPA. Through this request, Calwell received 220 reports, including some that were never sent to EPA, a violation of Federal law. In 1995, EPA fined Dow $876,000 for this violation.50
In 1994, the Attorney General for New York, Eliot Spitzer, sued Dow AgroSciences LLC for advertisement claims that their chlorpyrifos-containing product, Dursban was “safe.” Spitzer came to an agreement with the company that prohibited them from making such claims.51 Spitzer sued the company again in 2004 for violating that agreement, and Dow AgroSciences LLC was forced to pay a $2 million penalty, which was the largest such penalty ever paid for a case involving pesticide products at the time.52
On June 7, 2000, EPA and the registrants of chlorpyrifos came to an agreement to eliminate all household uses of the insecticide, except for roach baits and ant mound treatments, because of dietary and non-dietary risks, specifically to children.24 The agreement also discontinued the use of chlorpyrifos on tomatoes and restricted the uses of chlorpyrifos products on apples and grapes, as these three foods are all eaten in higher quantities by children.38 This agreement went into effect in 2001 during the re-registration process (66 FR 34184).53 This was in part a result of the FQPA, which required EPA risk assessments to include a safety factor that is tenfold greater for children, to account for their unique susceptibility to pesticides.54 Since these reductions in chlorpyrifos uses occurred during their research study, the scientists at Columbia were able to examine whether or not this agreement had any effect on exposure levels in New York City children. They did find that levels declined in their cohort after 2001 and were largely non-detectable by 2006.55 In 2002, EPA introduced new changes to protect the safety of farmworkers applying chlorpyrifos through an Interim Reregistration Eligibility Decision (IRED). These included reducing the number of time per season that chlorpyrifos could be applied and increased the amount of PPE required to be worn.38
In 2006, EPA re-registered chlorpyrifos and released a cumulative risk assessment for organophosphate pesticides56, as required by the FQPA clauses that require 10-year reviews of pesticide tolerances. EPA concluded from this review that the organophosphates do not exceed the level of concern necessary to take regulatory action.2
In 2007, the Pesticide Action Network North America (PANNA) and Natural Resources Defense Council (NRDC) petitioned EPA ban chlorpyrifos through a cancellation of all registrations and revocation of all tolerances, based on a preponderance of evidence demonstrating that the insecticide poses unreasonable harm to human health.57 They claimed that the 2006 cumulative risk assessment did not consider new scientific studies that demonstrated harm caused by chlorpyrifos exposure. The petition also points out that the critical endpoint used for the cumulative risk assessment for organophosphate pesticides was cholinesterase inhibition in blood cells, while the critical endpoint most relevant for chlorpyrifos is alterations to the structure of the brain during development. They go on to argue that the 10x safety factor dictated in FQPA for children is inadequate because there is no known safe level of chlorpyrifos exposure for developing brains. However, EPA used a 1x FQPA factor because no demonstrated evidence of difference between adult rats and pups for the endpoint they chose—cholinesterase inhibition. In considering aggregate risk (risk due to multiple exposure routes), EPA did not consider inhalation exposure, which the petitioners argue is an important exposure route for those near fields where chlorpyrifos has been applied because of spray drift and the volatility of chlorpyrifos.58 Another criticism the petitioners provide of the organophosphate risk assessment is that the intra-species variability factor applied (10x) was inadequate based on evidence in humans59 that PON1 status (a biomarker of sensitivity to organophosphate toxicity) is responsible for an up to 164x variation in human susceptibility to chlorpyrifos, meaning that two humans can experience an 164-fold difference in toxicity following exposure to chlorpyrifos. The petitioners argue that using this larger variability factor would produce tolerance levels that would be below of the level of detection. This, they stated, is reason enough to revoke all tolerances.
EPA allowed for a two-month public comment period on this petition,60 of which there was support and opposition among the approximately 90 comments submitted. Additionally, EPA documents indicate that between 2008 and 2012, EPA employees were receiving feedback from members of the Scientific Advisory Panel (SAP) over the course of five SAP meetings.2 Two of these meetings, in 2008 and 2011, were reported publicly.61 However, EPA did not make a final decision regarding the petition, so three years later, the groups filed a lawsuit in the Southern District of New York against EPA (NRDC v. EPA, No. 10.cv.5590) because of the unreasonable delay responding to the petition.62 The plaintiffs argued that this delay violated the Administrative Procedure Act (60 Stat. 237). In response to this lawsuit, EPA agreed to conduct another risk assessment and respond formally to the 2007 petition by November 2011.63
In 2011, as part of the standard registration review process, EPA published a Preliminary Human Health Risk Assessment for chlorpyrifos, in which the agency incorporated new research findings since the last assessment in 2000, which resulted in the voluntarily cancellation of household uses. In this updated risk assessment, a FQPA safety factor of 1x was applied for oral exposures and cholinesterase inhibition was the critical endpoint.64 Also in 2011, the EPA removed the 1998 Integrated Risk Information System (IRIS) reference dose (RfD) value from their website. The RfD was originally published as 0.003 mg/kg-day, which was based on decreased plasma cholinesterase.65
In 2012, the EPA released a Spray Drift Mitigation Decision to reduce potential exposures among those living and working near areas with aerial chlorpyrifos application. This decision included the introduction of “no-spray” buffer zones around specific buildings and areas, like schools and parks.66 In December 2014, EPA released a Revised Human Health Risk Assessment, an update to the 2011 risk assessment, both part of the registration review process. In this risk assessment, EPA included inhalation exposures and incorporated new information on potential spray drift exposure. EPA also used a FQPA safety factor of 10x instead of the previously used 1x and the critical endpoint was acetylcholinesterase (AChE) in blood.38
On September 10, 2014 PANNA and NRDC submitted a renewed writ of mandamus (renewing one submitted in April 2012 that was denied by the court) because of EPA’s continued delay in responding to the 2007 petition.67 In essence, this request was to the court to force EPA to respond to the original petition by either December 2014 or summer 2015. By June of 2015, EPA indicated to the court that it intended to issue a proposed rule that would revoke all tolerances sometime in summer 2016, following an updated assessment of drinking water.2 On August 10, 2015, the Ninth Circuit Court that was hearing PANNA v. EPA issued an order to EPA to respond to the 2007 petition by October 31, 2015, later than originally requested by PANNA and NRDC but earlier than proposed by EPA.63
On November 6, 2015, EPA issued a proposed rule to revoke all of the tolerances for chlorpyrifos, stating that they could not “conclude that the risk from aggregate exposure from the use of chlorpyrifos meets the safety standard” under FFDCA based on the findings of their 2014 risk assessment.68 Over 90,000 comments were submitted during the public comment period. On December 10, 2015, the Ninth Circuit court ordered EPA to issue a final rule by the end of 2016. In June 2016, EPA requested a six-month extension to that deadline because of the conclusions from a SAP meeting in April 2016, but the court only granted them a three-month extension, making the final deadline March 2017.69
In April 2016, EPA convened a meeting of the FIFRA SAP to discuss the biomonitoring data from epidemiological studies, like the ones conducted at Columbia under Dr. Virginia Rauh. At this meeting, the SAP discussed the EPA’s proposal to change the critical endpoint from AChE inhibition to impaired neurodevelopment (based on studies by Dr. Rauh and colleagues), as discussed in the 2007 PANNA petition. In their review, the SAP raised a few concerns regarding the EPA methodology for evaluating risk of chlorpyrifos exposure and the methods for incorporating the Columbia studies. In short, the Panel was not confident in the exposure data used by the Columbia researchers (maternal cord blood levels), and therefore not confident in the point of departure (PoD) derived from those studies. The panel members argued that they couldn’t adequately assess the quality of the Columbia research and would like to see the results replicated. The Panel recommended a PoD for adverse neurodevelopment that is based on time-weighted average prenatal blood chlorpyrifos levels. Finally, in opposition with the argument presented in the 2007 PANNA petition, the SAP agrees with EPA’s decision to use a 10-fold intra-species variation factor.70
On November 10, 2016, in response to the SAP review, EPA released a revised Human Health Risk Assessment that used neurodevelopmental outcomes instead of AChE inhibition and based the PoD on estimated prenatal exposure rather than maternal blood levels at delivery. EPA maintained using a 10x intraspecies uncertainty factor in this risk assessment.69 EPA maintained the proposed rule revoking all chlorpyrifos tolerances after concluding that the findings of this revised risk assessment did not differ from the 2014 risk assessment. A Notice of Data Availability was published on November 1771 and the public comment period ended on January 17, 2017, three days before Donald Trump was inaugurated as president.
The March 2017 deadline set by the Ninth Circuit for a final rule fell within the second month of a new presidential administration, giving the new president and EPA Administrator the authority to issue a final rule or deny the petition altogether. On March 29, 2017, EPA under the leadership of newly-appointed Administrator Scott Pruitt reversed the decision made under the prior presidential administration to revoke all tolerances and denied the 2007 petition, maintaining all uses and tolerances of chlorpyrifos.72 In a statement, Administrator Pruitt referred to this decision as a “return to using sound science in decision-making.” The EPA press release on the day of the decision emphasizes the heavy reliance of the agricultural sector on chlorpyrifos and the uncertainty surrounding the epidemiological data used by EPA in the 2015 proposed rule.72
On April 5, 2017, PANNA and NRDC once again petitioned EPA to ban chlorpyrifos (Pesticide Action Network North America; Natural Resources Defense Council, Inc., v. U.S. Environmental protection Agency, U.S. Court of Appeals, Ninth Circuit, 14-72794), this time on the basis that the denial of their 2007 petition was not based on any new findings of safety. This time, the Ninth Circuit rejected the petition.73 Similarly, the same environmental groups along with others filed a challenge of EPA’s decision (League of United Latin American Citizens v. Scott Pruitt, U.S. Court of Appeals, Ninth Circuit, 17-71636) on June 5, arguing that the 2015 EPA proposed rule to revoke all tolerances concluding that exposure to the pesticide was unsafe, thereby requiring EPA to ban it. The attorneys general of seven states (Maryland, California, Massachusetts, Maine, New York, Washington, Vermont) are seeking to join this lawsuit.74 On July 25, 2017, U.S. Senator Tom Udall introduced Protect Children, Farmers, and Farmworkers from Nerve Agent Pesticides Act of 2017 (S.1624), which would ban chlorpyrifos in the United States.75 In February 2018, a bill (SB3095 SD1 HD1 CD1) was introduced in the Hawaiian state legislature that would ban the use of chlorpyrifos on all of the islands effective January 1, 2019.76
4. Conclusions
The history of chlorpyrifos regulation is important to know for environmental health researchers and advocates. For one, it is always important to understand the long, arduous process required to revoke tolerances or cancel registrations of potentially harmful pesticides. It is also important to understand the value of petitioning EPA, as was done by PANNA and NRDC. While we do not know what would have happened without the 2007 petition, the arguments made in their petition were considered and eventually incorporated into EPA’s updated risk assessments. Understanding FIFRA is also important for consumers and farmworkers, as the decisions made by EPA in the face of scientific uncertainty directly affect their exposures to pesticides.
5. Proposed Policy Changes
In order to better protect public health through reducing exposures to hazardous pesticides, I propose the following:
• Congress should grant EPA the authority to increase fines for instances of failed reporting of adverse incidents of pesticide exposure collected by registrants
• Congress should grant EPA the authority to increase FIFRA registration fees which would fund the salaries of additional risk assessors in order to review and update pesticide registrations at a shorter frequency (particularly those assessed to have high exposure levels)
• As epidemiological studies are not possible until after a pesticide has been registered, Congress should increase National Institute of Health budget to allow for increased funding for studies on the health effects of exposure to widely used pesticides in humans (a specific focus should be on exposure to pesticide mixtures and low-dose, chronic exposure scenarios)
• Congress should amend FIFRA to remove the benefit consideration for pesticide cancellations on the basis of residential, occupational or ecological risks
• Congress should amend FFDCA to grant FDA the authority to more strictly enforce violations of pesticide tolerances
• Congress should not pass the HONEST Act (H.R. 1430), which would severely limit the amount of peer-reviewed studies that could be considered in EPA rulemaking
• Congress should repeal or amend the Congressional Review Act of 1996 (5 USC Ch. 8) to prevent future Congresses from revoking EPA rules passed under prior administrations, which could have been another mechanism for preventing a chlorpyrifos ban had it been finalized before January 2017
• EPA should not adopt proposed policies that are in line with the H.R. 1430 which would require the data for all studies used in Agency decisions to be made publicly available, severely restricting the amount of epidemiological evidence that can be used in EPA decisions
• EPA should consistently update and revise the “Framework for Incorporating Human Epidemiologic & Incident Data in Risk Assessments for Pesticides” to fine-tune the process for incorporating human epidemiological data into pesticide risk assessments
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