Recent Independent Scientific Review
Among pesticides, chlorpyrifos receives considerable research interest, in part because there has already been a great deal of research on the product (so future researchers already have the groundwork laid for them). The product is also of ongoing interest because, as a result of its broad usage on crops, human exposures to trace levels are common.
Below are summaries of recent independent evaluations of studies conducted on the effects of chlorpyrifos. At the end of each summary, you can link to or download the published study in its entirety.
FIFRA Scientific Advisory Panel Report on Chlorpyrifos, September 2008
Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the EPA is required to review older pesticides to ensure they meet both scientific and regulatory standards. FIFRA’s Scientific Advisory Panel (SAP) is a Federal advisory committee, apart from the EPA, whose purpose is to review pesticides and pesticide-related matters the EPA must act on. The FIFRA SAP considers information provided by the EPA, as well as from public comment periods and provides the EPA with peer-reviewed expert advice and recommendations regarding the human health and environmental impact of pesticides.
In anticipation of the Registration Review of chlorpyrifos, EPA announced in April 2008 that it was updating the hazard identification and characterization of chlorpyrifos. To facilitate this process, EPA held a FIFRA Science Advisory Panel in September 2008 to consider and review certain aspects of a substantial amount of research on the human health effects of chlorpyrifos that has been developed over the past decade, especially studies of chlorpyrifos’ effects on animal and human health, and scientific methods used to design and conduct these studies.
Minutes of the SAP meeting on chlorpyrifos were published in December 2008. Some of the Panel’s key findings are as follows:
- Cholinesterase inhibition1 is currently the most sensitive biomarker of chlorpyrifos exposure and, as such, should continue to be used for study until alternatives are identified and scientifically validated.
- Because of their various limitations, currently-available epidemiological studies of newborn and young children should not be used as the principle basis for setting exposure standards.
- While greater sensitivity to chlorpyrifos has been demonstrated in young animals with acute, high-dose laboratory exposures, young animals are not more sensitive to low-dose repeated chlorpyrifos exposures, even at doses well in excess of EPA limits.
- There is no one-to-one correspondence between chlorpyrifos exposure and levels of TCP (TCPy)2 in urine.
Read the full technical report
Eaton Review of Scientific Studies on Chlorpyrifos
In September 2008, the journal Critical Reviews in Toxicology published an extensive review of thousands of studies on chlorpyrifos. This review was conducted by an international panel of 13 highly-respected physicians, medical scientists, toxicologists, and epidemiologists, with relevant expertise in fields such as pediatric neurology, neurotoxicology, and child psychiatry.
The study was sponsored (funded) by Dow AgroSciences and managed through Science Partners LLC, an independent scientific partnership comprised of 150 of the United States’ and Europe’s top scientists. Science Partners LLC ensured that its scientists were provided independence in their research on chlorpyrifos and that their findings would be published, regardless of the outcome — and regardless of whether or not those findings had the approval of clients and funders.
Key points from the panel’s review include:
- Past estimates of chlorpyrifos exposure using TCPy measurements in urine overestimated those exposures by a factor of 10 to 20 times.
- Chlorpyrifos exposures from oral ingestion (dietary sources) is estimated to fall “substantially below” acceptable levels established by the EPA.
- Animal studies using doses substantially greater than consumers might encounter have not identified significant developmental effects in female rats and mice.
- While there are some studies that report possible associations among children between chlorpyrifos and some measures of newborn health (e.g. birth weight, head size, etc.), the weight of the evidence does not support a direct cause-and-effect relationship.
- Available data have not demonstrated that currently-allowed exposures to chlorpyrifos alter brain development.
Read the press release
Access the Eaton et al. review:
California Review of Chlorpyrifos for Listing Under Proposition 65
In late 2008, a group of California health and medical experts convened by California regulators as the Developmental and Reproductive Toxicant Identification Committee (DARTIC) determined that chlorpyrifos would not be listed as a developmental or reproductive toxicant under California’s Proposition 65 (The Safe Drinking Water and Toxic Enforcement Act of 1986). The panel evaluated the database for chlorpyrifos, including the findings of recent studies. Noting discrepancies between the results of animal vs. human research, the panel found inconclusive evidence that developmental or reproductive toxicity resulted from anticipated exposures to the product. Read the transcript of the meeting.
2TCPy (also called TCP) is a metabolite — in other words a breakdown product — of chlorpyrifos and other pesticides. It can be found in urine and is used by some researchers to estimate how much of the original pesticide was processed by the body.
