Federal Agencies release Technical Report on Toxic Contaminants in the Chesapeake Bay and its Watershed

February 28. 2013 16:56

The report: Toxic Contaminants in the Chesapeake Bay and its Watershed: Extent and Severity of Occurrence and Potential Biological Effects summarizes information on the extent and severity of occurrence of toxic contamination in the Bay and its watershed. The report includes a section on impacts of pesticides and pesticide use that warrants comment.

CropLife America (CLA) is a not-for-profit trade organization representing the nation’s developers, manufacturers, formulators and distributors of plant science solutions for agriculture and pest management in the U.S. Our member companies produce, sell and distribute virtually all the crop protection technology products used by American farmers. CropLife America comments on issues that are of interest to its member companies.

CropLife America members work with farmers and ranchers everyday to ensure that pesticides and crop protection tools are registered properly and used correctly. America’s abundant, affordable food supply depends on the availability of safe, effective crop protection products – moreover, our ability to help ‘feed the world’ centers on the efficiency and ingenuity of modern agricultural technology like pesticides. The ability to provide these products to our nation’s farmers hinges on a transparent, rigorous, science-based review process that is well-established under FIFRA that considers the risks as well as the benefits of crop protection products.

The report states that “data and research gaps exist for many pesticides including some current-use and some legacy pesticides, and consequently the extent and severity remains uncertain and cannot be evaluated at this time. For example, the potential sublethal effects of low concentrations of many pesticides (and degradates) and their mixtures (including adjuvants, etc.) in the environment is poorly understood”.

Pesticide products are subject to rigorous regulatory review and extensive testing prior to gaining regulatory approval for commercial use. As a result, there exists for pesticide products an abundance of information relative to other industrial chemicals. A dossier submitted to the Agency for the registration of a new pesticide product will typically be more than 30,000 pages in length including the reports of more than 126 studies involving 30 or more species that are required for registration. This rich data environment provides OPP with the opportunity for a level of sophistication in the estimation of risk that is typically unavailable to other branches of government in conducting risk assessments. When the EPA OPP have a specific risk concern based on additional information, they have the legal authority to ask for more data. Which is something they do routinely. The fate and effects of agricultural chemicals are not poorly understood.

For mixtures, toxicity and risk depend not only on the concentration and frequency of exposure, but also on the potential for, and probability of, interactive effects of the chemicals in an organism. The potential for interaction is dependent on the mechanism of action and pharmacokinetics; the absorption, metabolism, disposition, and elimination of the compounds, as well as their likelihood of co-occurrence at levels high enough for any observed interaction to occur (Moore, 2012; Teed and Moore, 2012). Laboratory experimentation with mixtures suggests in the wide majority of instances, that dose addition conservatively estimates potential toxicity. Dose addition typically overestimates the toxicity of mixtures of chemicals with dissimilar modes of action. An additive response also depends on the relative potency of the constituents of the mixtures, similarities and differences in pharmacokinetics and the selected dose relative to the effective dose – as noted in the Chesapeake Bay toxics report; co-occurrence in the field is often observed at levels below toxicity thresholds. Synergism of chemical activity, leading to an observed response greatly exceeding what would be expected from dose addition, is a very rare event.

Testing of the acute toxicity of pesticide formulations to mammals is a requirement of registration. This informs an assessment of risk due to occupational exposure. The toxicity of formulated products in the aquatic environment is less of a risk concern, since formulated pesticides are not completely transported to a body of water, except by spray drift or deliberate application to water bodies for weed or insect control. Adjuvants, other inert ingredients and active ingredients usually differ regarding their adsorptive properties and biotic/abiotic degradation rates, which cause them to separate before they reach an aquatic environment. The co-occurrence in the environment of components of a pesticide formulation in the same proportion as they appear in a formulated product would be a rare event. A comparative analysis of the aquatic toxicity of ai ingredients to the toxicity of formulated products determined that the toxicity of the majority of formulations was less than or equal to the toxicity that would be attributed to the a.i. alone (Schmuck et al., 1994).

While data suggest that unintentional environmental mixtures of pesticides are a common occurrence in areas where the landscape is dominated by agriculture, the pesticide concentrations in the nation’s waters are generally minute. The reports cites the USGS National Water Quality Assessment (NWQA) program data which indicates that “more than 6,000 unique 5-compound mixtures were found in samples from agricultural streams”; this number decreases to “less than 100 when only concentrations greater than 0.1 ppb are considered”. Further, “pesticide concentrations are below 0.1 part per billion (ppb) in 80% of the surface water samples, and below 1 ppb in 95% of the samples”. Even though the most frequently found pesticides can be identified, this list varies by location, local land use and pesticide use, and setting (urban versus agricultural).

The report notes that the total mass of pesticides being applied to the Chesapeake Bay watershed declined during the period 1985 to 2004; however, because the potency of these chemicals increased notes that during the same period, the “toxic units” remained approximately static or increased depending on the bioassay test organism(s) used Hartwell (2011). It makes little sense that the reductions in use, the greater specificity inherent in the newer products being used and the opportunity to apply at lower rates does not translate to an overall environmental benefit.

The total lands under agricultural production in the U.S. have diminished, however there have simultaneously been large production gains with fewer inputs (NASS statistics on total farm inputs). This is largely due to better and more efficient use of agricultural technology, including use of pesticides, fertilizer and water through applied agricultural engineering and agronomy. Applications of pesticide products have become more sophisticated and application technology in agricultural and urban settings has continually improved to increase efficiency. Examples are: the development and use of low drift nozzles for sprayers: formulation technologies for controlled release, better crop penetration, and better seed treatments; the use of resistance engineered plants; and application equipment with variable rate controls linked to GPS systems that eliminate overspray and automatically shut off around corners or near streams. The environmental benefit of this is that less product gets used and less of the product is available to move out of the intended area of application, like into the Chesapeake or its tributaries.
The report notes that the US EPA Office of Pesticides Program Aquatic Life benchmark for atrazine is 65 micrograms per liter (µg/L); however, Tillitt et al. (2010) showed that chronic exposures to concentrations as low as 0.5 µg/L will cause fathead minnows to spawn less frequently and to produce fewer eggs than controls.” It was not noted in the report that the results reported by Tillitt et al. (2010) are inconsistent with the results of 4 fish full life cycle studies submitted to EPA which report no effects on reproduction, two of which were for the same species (fathead minnow) of fish. These 4 studies were conducted using a standard protocol, accepted by the USEPA. They are of much longer duration (274-450 days) and much higher atrazine exposures (maximum exposures 95 to 2000 ppb) and fish are continuously exposed to the test product from an early life stage (embryo/larval/juvenile) throughout development and reproductive stages until a pre-determined number of spawns occur. There were anomalies in the control egg production highlighted in the Tillett study that undoubtedly influenced the outcome of the study. It is unclear why the EPA would highlight this study in the Chesapeake Bay toxics report and not acknowledge other studies that refuted the study results.
The report states that “many other studies have concluded that conventional benchmarking approaches to decision making are inadequate for a variety of reasons. For example, Fatima et al. (2007) exposed goldfish to environmentally relevant mixtures of herbicides (atrazine, simazine, diuron, and isoproturon) and observed biomarkers indicative of immune suppression. They concluded that these common environmental exposures cause immune suppression in goldfish, thereby representing an endpoint and exposure scenario that are not quantified in conventional benchmarking studies.”
The statement by Fatima et al (2007) that goldfish were exposed to environmentally relevant concentrations of this mixture of herbicides is clearly incorrect. Goldfish were exposed to a mixture of herbicides each with a concentration of 50 µg/L or a total herbicide concentration of 200 µg/L, for up to 12 weeks. Exposures are typically related to runoff events and concentrations decline rapidly. Exposure to even one of the herbicides at 50 µg/L for a period of weeks would be unexpected. Exposure to this mixture at 200 µg/L would be virtually impossible. This is supported by the monitoring data for atrazine contained in the Draft Report itself. Furthermore, these compounds have the same mode of action (inhibition of photosynthesis at photosystem II) but differing major uses and use regions. A scenario in which these 4 similar herbicides are used concurrently within the same watershed, is very unlikely. To state that this study examined an environmentally relevant mixture is inaccurate.
Similarly, the statement that the Rohr et al. (2008) exposures were environmentally relevant is misleading. As demonstrated by statements within the report, an exposure dose of 200 µg/L is not environmentally relevant.
The Hayes study was examined in 2003 by a Scientific Advisory Panel (SAP) of the USEPA and found to be flawed and inconclusive. In 2007 EPA concluded “that atrazine does not adversely affect amphibian gonadal development based on a review of laboratory and field studies, including studies submitted by the registrant and studies published in the scientific literature.” (EPA, 2007). In 2010 EPA reiterated that “…atrazine does not adversely affect amphibian gonadal development based on a review of laboratory and field studies...no additional testing is warranted to address this issue.” (EPA, 2010). Finally, in 2012 the White Paper published by EPA prior to the SAP in June indicated no compelling evidence to change the position from 2007-2010. It is unclear why this EPA sponsored report would contain statements diametrically opposed to EPA pronouncements on thorough investigation of the issue as well as the conclusions of EPA science peer review.
Thank you for the opportunity to comment on this report. We welcome the opportunity to work with the Chesapeake Bay Committee in the future.
Sincerely,

Michael Leggett, Ph.D.
Sr. Director Environmental Policy
CropLife America
EPA, 2007a. 40 CFR Parts 9, 152, 156, 159 et al. Pesticides; Data Requirements for Conventional Chemicals, Technical Amendments, and Data Requirements for Biochemical and Microbial Pesticides; Final Rules. Part II, Environmental Protection Agency. Federal register/Vol. 72. No. 207/Friday, October 26, 2007/Rules and Regulations: 40 CFR EPA-HQ-OPP-2004-0387-0160[1].
EPA, 2010a. Judkins, D.R. and Wolf, J.K. Risks of Simazine Use to Federally ThreatenedDelta Smelt (Hypomesus transpacificus). Pesticide Effects Determinations PC Code: 080807 CAS Number: 122-34-9 Environmental Fate and Effects Division Office of Pesticide Programs Washington, D.C. 20460 June 30, 2010. 105 pages.
EPA, 2010b. Sankula, S and Lin, J. Risks of Metolachlor and S-Metolachlor Use to Federally Threatened Delta Smelt (Hypomesus transpacificus) and California Tiger Salamander (Ambystoma californiense) (Central California Distinct Population Segment) and Federally Endangered Sonoma County and Santa Barbara County Distinct Population Segments of California Tiger Salamander Pesticide Effects Determinations PC Codes: 108801 (Metolachlor) and 108800 (S-Metolachlor) CAS Numbers: 51218-45-2 (Metolachlor) and 87392-12-9 (S-Metolachlor) Environmental Fate and Effects Division Office of Pesticide Programs Washington, D.C. 20460 29 June 2010. 143 pages.

Mike Leggett