Alexis Pieter Roodt

• Adult emerging aquatic insects can transfer micropollutants, accumulated during their aquatic development, from aquatic to terrestrial ecosystems. This process depends on both contaminant- and organism-specific properties and processes. The transfer of contaminants can result in the dietary exposure of terrestrial insectivores at the aquatic-terrestrial ecosystem boundary. It is, however, unknown whether this route of contaminant transfer is relevant for current-use pesticides, despite their ubiquity in freshwater ecosystems globally. Furthermore, empirical investigation of pesticides in terrestrial insectivores which consume emerging aquatic insects (e.g. riparian spiders) is lacking. In the present work, two laboratory batch-scale studies and a field study were conducted to investigate the transfer of current-use pesticides by emerging aquatic insects and the dietary exposure of riparian spiders preying on emerging insects. In the two laboratory studies, larvae of the model organism, Chironomus riparius, were exposed, either chronically to seven fungicides and two herbicides, or acutely (24-hours) to three individual insecticides during their development. The pesticides were all small organic molecules, selected to cover a low to moderate lipophilicity range (logKow 1.2 – 4.7). Exposure took place at three environmentally relevant concentrations for the fungicides and herbicides (1.2 – 2.5, 17.5 – 35.0 or 50.0 – 100.0 ng/mL) and two for the insecticides (0.1 and either 4 or 16 ng/mL). Eight of the nine fungicides and herbicides, as well as one of the three insecticides were detected in the adult insects after metamorphosis. Concentrations of the pesticides decreased over metamorphosis. However, the transfer of individual pesticides was not well predicted using published models which are based on contaminant lipophilicity andwere developed using other contaminant classes. In the present work, pesticide-specific differences in bioaccumulation by the larvae, retention through metamorphosis and sex-specific bioamplification and elimination over the course of the terrestrial life stage were observed. The neonicotinoid, thiacloprid, was the only insecticide retained by the emerging insects, due to its slow elimination by the larvae. Thiacloprid also decreased insect emergence success. An approximate 30 % higher survival to emergence in the low exposure level (0.1 ng/mL), however, resulted in a relatively higher insecticide flux, from the aquatic to the terrestrial environment compared to the higher exposure (4 ng/mL). For the field study, a method for the analysis of 82 current-use pesticides by high-performance liquid chromatography tandem to triple quadrupole mass spectrometry using small volumes (30 mg) of insect material was validated and applied to samples of emerging insects and Tetragnatha spp. spiders which were collected from stream sites impacted by agricultural activities. Emerging aquatic insects from three orders (Diptera, Ephemeroptera and Trichoptera) contained 27 pesticides whereas 49 pesticides were found in the aquatic environment (water, sediment and aquatic leaf litter). This included mixtures of up to four neonicotinoid insecticides in the insects, with concentrations up to 12300 times greater than were found in the water. Furthermore, the web-building riparian spiders contained 29 pesticides, generally at low concentrations, however concentrations of three neonicotinoids and one herbicide were biomagnified compared to the emerging insects. The three studies included in this thesis thus reveal that the aquatic-terrestrial transfer of current-use pesticides occurs, even at very low environmentally relevant exposure concentrations. Furthermore, new knowledge was generated on the diverse interactions between current-use pesticides and organisms over their entire lifecycles, affecting the propensities for individual pesticides to be transferred via insect emergence. A wide range of pesticides were found to be dietarily bioavailable to riparian spiders, and likely many other riparian insectivores. The neonicotinoid insecticides stood out for their potential to negatively impact adjacent terrestrial food webs through negative impacts on aquatic insect emergence (i.e. biomass flux), while still having a high propensity to be transferred by emerging insects and bioaccumulated in riparian spiders.