Using the Pesticide Toxicity Index to show the potential ecosystem benefits of on‐farm biobeds

Abstract

The influent and effluent of two single-cell biobeds (Province of Alberta, Canada) and two dual cell-biobeds (Province of Saskatchewan, Canada) were monitored during a number of growing seasons. A total of 59 unique pesticide active ingredients were detected, with all biobed influent samples (n = 54) and 93% of effluent samples (n = 54) containing pesticide mixtures. About one-half of the effluent samples in both single-cell (56%) and dual-cell (45%) biobeds contained active ingredients that have Groundwater Ubiquity Score (GUS) values >2.8 and so were more likely to move through the biomatrix materials into effluent. The Pesticide Toxicity Index (PTI) calculated for aquatic indicator species (i.e., vascular and nonvascular plants, invertebrates, and fish) was always larger for influent samples (e.g., median PTI >500 for invertebrates in dual-cell biobed) than effluent samples (i.e., median PTI <1). As such, this study demonstrates the potential ecosystem benefits of the broad adoption of on-farm biobeds in the Canadian Prairies for recycling tank rinsate as a strategy to accelerate a green economy. Although biobeds were highly effective in reducing the concentrations for pesticides with a wide range of soil organic carbon coefficient and half-life values, the biobed effectiveness was relatively poor for the herbicides clopyralid, diclofop, fluroxypyr, and imazethapyr. Clopyralid (3.02), fluroxypyr (3.70), and imazethapyr (3.90) all have relatively high GUS values (>2.8) and are thus more likely to be detected in effluent than active ingredients with smaller GUS values. This suggests that further improvements in biosystem design need to be made for optimizing the recycling of these pesticides. INTRODUCTIONPesticide handling areas result in point-source pollution that can account for up to 90% of the total pesticide loadings in water resources (Frede et al., 1998;Neumann et al., 2002). By capturing the pesticide residues associated with the filling and cleaning of spraying equipment, biobeds are designed Abbreviations: 2,4-D, 2,4-dichlorophenoxyacetic acid; DT 50 , soil pesticide half-life; GUS, Groundwater Ubiquity Score; MCPA, 2-methyl-4-chlorophenoxyacetic acid; PTI, Pesticide Toxicity Index.

On-Farm Removal of Pesticides: Current Insights on Biopurification Systems

“…Acute tests, probably due to their faster, cheaper, and in general easier protocols, have been employed more often than chronic tests, basically applying the immobilization test in the microcrustacean Daphnia magna , , mortality tests in the earthworm Eisenia andrei , the annelid worm Enchytraeus crypticus , and the springtail Folsomia candida − as well as the inhibition of bioluminescence in Vibrio fischeri . Chronic assays so far applied include reproduction tests in the same organisms used for acute determinations, and metabolic alterations in the fish Oreochromis aureus ; ,, similarly, phytotoxicity determined by germination tests in the plant Lactuca sativa has been seldom applied. ,,,, Alternative approaches such as the use of pesticide toxicity index (PTI), which employs ecotoxicological parameters from aquatic indicator species (i.e., vascular and nonvascular plants, invertebrates, and fish) rather than direct tests, have been used to determine detoxification of BPS effluents. As expected, the usefulness of these benchmark organisms depends on the functional nature of the pesticides removed in the BPS; i.e., the daphnids are expected to be more sensitive to insecticides, and the phytotoxicity tests are more appropriate for herbicides.…”

“…Overall, such data highlights the importance of employing a large battery of benchmark organisms, not only in acute but also in chronic assays, to properly estimate and monitor the residual toxicity of a BPS. In this respect, the use of the pesticide toxicity index (PTI) may act as a useful complement to ecotoxicological evaluation to define the performance of BPSs. , Furthermore, ecotoxicological evaluation should become a key factor when it comes to deciding the disposal approach of old biomixtures, as discussed in Section 6.…”

“…50 Chronic assays so far applied include reproduction tests in the same organisms used for acute determinations, and metabolic alterations in the fish Oreochromis aureus; 47,48,51 similarly, phytotoxicity determined by germination tests in the plant Lactuca sativa has been seldom applied. 22,23,40,52,57 Alternative approaches such as the use of pesticide toxicity index (PTI), which employs ecotoxicological parameters from aquatic indicator species (i.e., vascular and nonvascular plants, invertebrates, and fish) 53 rather than direct tests, have been used to determine detoxification of BPS effluents. As expected, the usefulness of these benchmark organisms depends on the functional nature of the pesticides removed in the BPS; i.e., the daphnids are expected to be more sensitive to insecticides, and the phytotoxicity tests are more appropriate for herbicides.…”

“…In this respect, the use of the pesticide toxicity index (PTI) may act as a useful complement to ecotoxicological evaluation to define the performance of BPSs. 53,60 Furthermore, ecotoxicological evaluation should become a key factor when it comes to deciding the disposal approach of old biomixtures, as discussed in Section 6.…”