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Daily News Blog

10
Apr

Study of Chemical Mixtures at Low Concentrations Again Finds Adverse Health Effects

Researchers find synergistic relationships in certain chemical mixtures, particularly heptachlor and triallate and trifluralin and lindane at lower concentrations, respectively.

(Beyond Pesticides, April 10, 2024) Researchers in a 2024 Chemosphere study find synergistic relationships in certain chemical mixtures, particularly heptachlor and triallate and trifluralin and lindane at lower concentrations, respectively. Investigators should consider additional binary data for acute toxicity and potential chronic health impacts on these mixture…which showed synergism at low levels,” the researchers conclude. “According to a Centers for Disease Control (CDC) assessment, more than 50 pesticides are detected in blood or urine samples from the US population,” Researchers point to a cause for concern. The findings come as no surprise to advocates who have urged an assessment of the potential synergistic impacts of pesticide mixtures in the regulation of pesticides.

Researchers “used the exposure data from a complex operating site with legacy pesticide pollution to evaluate if

  1. Inhalation of pesticide mixtures released from such contaminated sites could pose a risk to human health,
  2. The component-based risk assessment approaches that rely on additivity can predict the actual risk of pesticides in a mixture, and
  3. The legacy organochlorine pesticides banned many years ago interact with registered and supposedly safe herbicides in a mixture.”

The study site is “a pesticide packaging and handling facility” contaminated with the following pesticides (“historical and in current use”): 2,4-D (2,4-dichlorophenoxyacetic acid), 2,4-DB (4-(2,4-dichlorophenoxy)butyric acid), 2,4-DP (Dichlorprop), Aldrin, Bromacil, Bromoxynil, Chlordane, Clopyralid, DDD p,p, DDE p,p, DDT, o, p’, DDT, p,p’, Dicamba, Dieldrin, Dimethoate, Endrin, Heptachlor, Lindane, Malathion, MCPA, MCPP (mecoprop), Metribuzin, Treflan (Trifluralin), and Trilate/Triallate. “Only volatile COPCs (Henry’s Law Constant (H) greater than 10−5 atm m3/mol) in soil and groundwater were included in this study (triallate, trifluralin, lindane, heptachlor, dieldrin, and aldrin,” the researchers indicate in the Methods section. Quantitative risk assessment for pesticide exposure was rooted on oral exposure, which comes with potential uncertainties. For example, oral exposure tends to demand a higher dose to induce an identifiable adverse effect relative to inhalation exposure. In other words, using an oral reference dose may underestimate the potential risk.

Risk assessment of pesticide mixtures follows different logic systems depending on the research approach. As this study describes, “The default assumption is that at low concentrations, pesticides interact additively with one another; thus, the risk posed by each component of a complex mixture could be simply added up.” The binary weight of evidence, or BINWOE, builds on EPA’s approach at risk assessment through the interaction-based hazard index (HI Interaction). There was not enough published data on animal binary pesticide interaction which meant finding an alternative approach. Researchers used a cell line, SH-SY5Y, after a previous meta study found it to be an effective method to obtain relevant binary data that fits EPA’s HI Interaction approach while acting as a “predictive indicator” of adverse human health impacts to pesticide exposure.

Researchers did find values suggesting “significant health concerns” to toddlers, infants, teenagers, and adults in “commercial and industrial land use.” Additionally, there are several important takeaways from the study, including pivotal details on the synergistic impacts of chemical mixtures at different concentrations. “Nine of the 15 tested binary mixtures of pesticides synergistically reduced cell viability []. Seven mixtures (Trifluralin/Heptachlor, Trifluralin/Aldrin, Lindane/Heptachlor, Lindane/Aldrin, Heptachlor/Dieldrin, Heptachlor/Aldrin and Dieldrin/Aldrin) were synergistic at higher concentrations. However, two mixtures of herbicides and OCPs (Trifluralin/Lindane and Triallate/Heptachlor) interacted synergistically at lower concentrations. All binary mixtures of OCPs [organochlorine pesticides], except for Lindane/Dieldrin (additive at all concentrations), elicited synergistic effects at higher concentrations and additivity at lower concentrations.” Lindane, considered a legacy organochlorine, does in fact interact with “supposedly safe herbicides in a mixture.” The findings of this study, and similar findings in the scientific literature going back decades, demonstrate the importance of measuring the potential impacts of chemical mixtures in promulgating pesticide safety regulations.

The health consequences of chemical mixtures gained national attention in a recent dispute between the Office of the Inspector General (OIG) and the U.S. Environmental Protection Agency’s (EPA) Office of Pesticide Programs regarding the agency’s review of pet flea and tick collars. The OIG report indicated, “The EPA’s response to reported pesticide incidents involving Seresto pet collars has not provided assurance that they can be used without posing unreasonable adverse effects to the environment, including pets.”

Pollinators are also impacted by the mixture of toxic chemicals in the environment that are not evaluated by EPA for synergistic effects. A 2023 Nature study found a combination of insecticides and fungicides (including indoxacarb, spinosad, chlorpyrifos-ethyl, deltamethrin, dimethoate, imidacloprid, cyfluthrin, dithianon, etofenprox, and chlorpyrifos-methyl in 106 agricultural landscapes across Europe through identifiable adverse health impacts of bumble bees, signaling EPA and European environmental regulators’ failure to “safeguard bees and other pollinators that support agricultural production and wild plant pollination.” A 2014 study reached a similar conclusion regarding the synergistic effects in most pesticide combinations exacerbated pollinator mortality rates around the four-day mark of exposure. More concerning, however, were the results focusing on the allegedly “inert” ingredient, N-methyl-2-pyrrolidone. In this study, published in PLoS One, researchers indicate, “Even for the lowest concentration of [this inert ingredient], the estimated time to cause 50% larval mortality was 4 days.”

Given both the known and still unevaluated effects of pesticides, including the impact of mixtures and synergistic effects, and given the commercial viability and effectiveness of alternatives in both agricultural and nonagricultural use, Beyond Pesticides is calling for the phase out of toxic petrochemical pesticides by 2032. See the Gateway on Pesticide Hazards and Safe Pest Management to learn specific adverse health impacts of particular pesticide ingredients. See Pesticide-Induced Disease Database to peruse the latest scientific literature on pesticide exposure and health consequences. Safety Source on Pest Management Providers offers a list of pesticide application companies that avoid the use of toxic pesticides. To identify if you suspect that you or a loved one was or is being exposed to a harmful pesticide or chemical, see Pesticide Emergencies.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Source: Chemosphere

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