Probabilistic risk assessment of insecticide concentrations in agricultural surface waters: a critical appraisal

Abstract

Due to the specific modes of action and application patterns of agricultural insecticides, the insecticide exposure of agricultural surface waters is characterized by infrequent and short-term insecticide concentration peaks of high ecotoxicological relevance with implications for both monitoring and risk assessment. Here, we apply several fixed-interval strategies and an event-based sampling strategy to two generalized and two realistic insecticide exposure patterns for typical agricultural streams derived from FOCUS exposure modeling using Monte Carlo simulations. Sampling based on regular intervals was found to be inadequate for the detection of transient insecticide concentrations, whereas event-triggered sampling successfully detected all exposure incidences at substantially lower analytical costs. Our study proves that probabilistic risk assessment (PRA) concepts in their present forms are not appropriate for a thorough evaluation of insecticide exposure. Despite claims that the PRA approach uses all available data to assess exposure and enhances risk assessment realism, we demonstrate that this concept is severely biased by the amount of insecticide concentrations below detection limits and therefore by the sampling designs. Moreover, actual insecticide exposure is of almost no relevance for PRA threshold level exceedance frequencies and consequential risk assessment outcomes. Therefore, we propose a concept that features a field-relevant ecological risk analysis of agricultural insecticide surface water exposure. Our study quantifies for the first time the environmental and economic consequences of inappropriate monitoring and risk assessment concepts used for the evaluation of short-term peak surface water pollutants such as insecticides.

Agricultural insecticides threaten surface waters at the global scale

“…First, the published insecticide monitoring results to which we refer in our analysis most likely underestimate the actual exposure levels because it is extremely difficult to capture transient insecticide peak concentrations; ∼84.4% of the reported water-phase concentrations were measured using sampling strategies likely to miss the short-term insecticide peaks (20) ., 3-4) hours during ∼4-6 d/y coinciding with typical application patterns (e.g., in the spring/ summer). Organisms present at such sites receive their entire annual insecticide exposure dose during these short time periods during which short-term peak exposure incidents occur, and these incidents may cause long-term ecological perturbations (4,14) due to the high intrinsic toxicity of insecticides (6,26).…”

“…Therefore, our data show that the actual extent to which surface waters are contaminated with insecticides is not controlled effectively by increasingly stringent environmental regulations at present. However, in the LERQ countries, substantially larger surface water systems and longer sampling intervals were considered in the monitoring campaigns (SI Appendix, Table S11), decreasing the likelihood of determining insecticide peak exposure incidences (SI Appendix, Table S6) (20). The application of more targeted insecticide sampling strategies (20) is needed in the future to adequately reflect the risks to the surface waters of LERQ countries.…”

“…(i.e., less than 1% of the year) in agriculturally influenced surface waters. It follows that most traditionally operated, fixed intervalbased sampling campaigns inherently miss insecticide exposure (20). To avoid bias resulting from an excessive number of samples without quantifiable insecticide levels, exposure assessments of insecticides using monitoring data must be based solely on quantifiable concentrations in aquatic environments, i.e., those above the limit of quantification (LOQ) (SI Appendix, SI Discussion) (20).…”

Organic chemicals jeopardize the health of freshwater ecosystems on the continental scale

“…Third, other considerations, not addressed here, could exacerbate the chemical risk: (i) chemicals usually occur in mixtures, which have been shown to exhibit stronger combined adverse effects than single compounds, especially for chemicals with similar modes of action (11); (ii) transformation products may be more ecotoxicologically potent than their parent compounds (28); and (iii) current monitoring relies on point grab water samples at monthly or quarterly intervals, which are very likely to underestimate the real maximum concentrations (29). Moreover, very hydrophobic chemicals were omitted from the analysis due to uncertainty with regard to the effect concentrations derived from experiments exceeding the water solubility.…”

Environmental Risk Assessment of Agrochemicals — A Critical Appraisal of Current Approaches

“…Obviously, the accuracy of the SSD relies entirely on the number of species tested and the taxa covered in the dataset. Another criticism is that the actual concentrations measured in surface waters are typically underestimated because the peak concentrations of pesticides, which have the highest impact, are often missed, thus casting doubts about the reliability of the exposure predictions on which the probabilistic approach is based [100]. One solution is to build a cumulative graph of either measured or predicted environmental concentrations for different exposure scenarios, thus allowing estimation of probabilities of exposure in a similar way as the SSD [15].…”