Investigation of toxic effects of agrochemicals bound to fugitive beef cattle feedyard particulate matter to critical pollinator species
Insect-mediated pollination services are critical to many ecosystems around the world. Nearly 87% of angiosperms and almost a hundred cultivated food crops rely on wild or managed pollinators for reproduction or crop yield. Economic benefits of pollination services provided by animals globally are estimated up to $577 billion (USD) annually. These estimates are expected to continue rising in the future due to increasing human population and subsequent demand for food crop products. Unfortunately, between 20 – 40% of pollinator species around the globe are experiencing population decreases. The issue of pollinator decline is complex and contains a multitude of contributing factors. Chief among these are habitat loss, competition with invasive species, and exposure to toxic agrochemicals. Sensitivity to multiple classes of insecticides and parasiticides among pollinators is well documented. However, data regarding the toxic effects of agrochemicals bound to particulate matter (PM) is limited. The previously mentioned increasing human population has also driven an increase in demand for affordable, high-quality, protein-based foods, such as beef. This, in turn, has led to an increase in abundance and capacity of beef cattle feedyards in many areas of world. In the United States of America (USA), over twenty-six thousand feedyards contain over fifteen million head of cattle in a given year. Typically, feedyards are situated in arid to semi-arid environments, where precipitation is less than 510 mm per year on average. These dry, hot environments are conducive to wind-driven scouring of pen floor material (composed of cattle urine and feces), and subsequent dissemination into surrounding environs. Feedyard profitability and yield necessitates the use of a variety of veterinary pharmaceuticals, growth promoters, and pesticides to facilitate rapid muscle accretion and minimize losses due to pests. Residues of these chemicals are excreted by cattle in urine and feces or sequestered by pen floor material. When this contaminated material is disturbed by cattle activity it becomes suspended in the air and can be transported beyond feedyard boundaries, taking PM-bound agrochemicals with it. Multiple agrochemicals have been detected in relatively high concentrations in fugitive beef cattle feedyard PM. Data regarding the potential toxic effects of fugitive agrochemical-laden PM may exert on local pollinators is lacking. Here I present data generated from field- and laboratory-based experiments designed to bridge this data gap. First, honeybees (Apis mellifera) and blue orchard mason bees (Osmia lignaria) were exposed, in situ to agrochemical-laden PM emanating from feedyards. Second, I developed a method by which to simulate the conditions at feedyards and expose pollinators to PM under controlled conditions in a laboratory-based circulator system. Third, this method was used to conduct toxicity testing to determine the effects of individual agrochemicals bound to PM among three pollinators (honeybees, mason bees, and painted lady butterfly larvae (Vanessa cardui)). Honeybees and mason bees placed downwind of feedyards experienced significantly higher mortality compared to bees sited upwind of the same feedyards. Pollinator mortality in these experiments was positively correlated with toxicity-weighted concentrations (TWC) of seven commonly used agrochemicals (bifenthrin, permethrin, clothianidin, imidacloprid, thiamethoxam, abamectin, and ivermectin). Testing and verification of the novel PM circulation system revealed no significant increase in pollinator mortality due to agrochemical-free PM. Results of the toxicity tests conducted using the circulator system indicated significantly elevated mortality of all three pollinator species when exposed to environmentally relevant concentrations of individual agrochemical-fortified PM. Significantly elevated mortality of pollinators exposed to individual PM-bound agrochemicals implicates agrochemicals as the major driver of mortality observed in field experiments. Pollinator mortality in the circulator toxicity tests did not reach the magnitude observed in the field experiments, indicating additive or synergistic effects of agrochemical mixtures as an important contributor to mortality. Further, mortality was lower than expected, as the circulator exposure treatments far exceeded previously published contact toxicity benchmarks, suggesting limited uptake of PM-bound agrochemicals. Particulate matter emitted from beef cattle feedyards, and the many constituent agrochemicals contained therein pose a significant threat to local pollinators.