Biogeographical Analysis of Chemical Co‐Occurrence Data to Identify Priorities for Mixtures Research

Abstract

A challenge with multiple chemical risk assessment is the need to consider the joint behavior of chemicals in mixtures. To address this need, pharmacologists and toxicologists have developed methods over the years to evaluate and test chemical interaction. In practice, however, testing of chemical interaction more often comprises ad hoc binary combinations and rarely examines higher order combinations. One explanation for this practice is the belief that there are simply too many possible combinations of chemicals to consider. Indeed, under stochastic conditions the possible number of chemical combinations scales geometrically as the pool of chemicals increases. However, the occurrence of chemicals in the environment is determined by factors, economic in part, which favor some chemicals over others. We investigate methods from the field of biogeography, originally developed to study avian species co-occurrence patterns, and adapt these approaches to examine chemical co-occurrence. These methods were applied to a national survey of pesticide residues in 168 child care centers from across the country. Our findings show that pesticide co-occurrence in the child care center was not random but highly structured, leading to the co-occurrence of specific pesticide combinations. Thus, ecological studies of species co-occurrence parallel the issue of chemical co-occurrence at specific locations. Both are driven by processes that introduce structure in the pattern of co-occurrence. We conclude that the biogeographical tools used to determine when this structure occurs in ecological studies are relevant to evaluations of pesticide mixtures for exposure and risk assessment.

Variability of pyrethroid concentrations on hard surface kitchen flooring in occupied housing

“…These groupings indicate a non-random pyrethroid distribution among the houses which is consistent with the multipyrethroid cooccurrences structures found by Tornero-Velez et al 27 when analyzing hard surface wipe data collected from U.S. child care centers.…”

“…when analyzing hard surface wipe data collected from U.S. child care centers. According to Tornero‐Velez et al., these co‐occurrences reflect structuring processes such as availability of manufacturer formulations. However, because pyrethroids are frequently sold with only one or two active ingredients, it also suggests multiproduct usage by many of the households applying these insecticides.…”

A Pharmacokinetic Model of cis- and trans-Permethrin Disposition in Rats and Humans With Aggregate Exposure Application

“…Although permethrin is one of many pyrethroids on the market, it is frequently detected in agricultural commodities (USDA, 2009), and in homes and child care centers (Heudorf and Angerer, 2001;Schettgen et al, 2002;Tulve et al, 2006;Lu et al, 2006;Morgan et al, 2007;Tulve et al, 2008;Williams et al, 2008;Lu et al, 2009;Stout et al, 2009;Tornero-Velez et al, 2012), and its metabolites are detected in urine in the population (CDC, 2009). In the United States, permethrin is registered for use on numerous agricultural crops, livestock and livestock housing, modes of transportation, structures, public health mosquito abatement programs, and residential settings including use in outdoor and indoor spaces (U.S. EPA, 2006).…”

Assessing Risks to Endangered and Threatened Species from Pesticides

“…As discussed in Gilliom et al (2007, p.81), an analysis of the co-occurrence of pesticides might be useful in identifying environmental mixtures that have the greatest probability of adversely affecting listed species, and these investigators provide a preliminary assessment of the most commonly occurring mixtures of two to seven pesticides (Belden et al 2007). More detailed analyses of the frequency of the co-occurrence of pesticides have been used in human health risk assessments (e.g., Stackelberg et al 2009;Tornero-Velez et al 2012). The preliminary analyses by Belden et al (2007) on pesticides associated with corn and soybean production suggest that factoring the occurrence of environmental mixtures into assessments will increase the risk estimates but not substantially (by a factor of about 2).…”