Prioritization of currently used pesticides in soils of main European cropping systems and an Argentinian cropping system for assessment of mixture toxicity and risk on terrestrial biota

Abstract

Identifying driving compounds in mixture pressure on terrestrial organisms is crucial to assessing the possible risk of current-use pesticides. This study presents a scoring approach for the prioritization of pesticides occurring in real mixtures. Soil samples associated with eleven crop systems across Europe and Argentina were analyzed for approximately 200 pesticides and metabolites within the H2020-funded project SPRINT (Sustainable Plant Protection Transition: A Global Health Approach). The pesticides were ranked based on the frequency of detection in soil samples, risk quotient (RQ), and degradation rates. RQ was calculated using the regulatory ecotoxicological data, and Predicted Environmental Concentration (PEC) values were extracted from EFSA documents. The prioritization was conducted separately for soil invertebrates, bees and non-target arthropods (NTAs), non-target terrestrial plants, and microbes. To prioritize for ecotoxicity tests, the top five ranked pesticides for each crop scenario were considered as the most relevant environmental mixture for that crop scenario. Overall, pesticides of concern were related to their specific targeted chemistry, e.g. herbicides affected plants the most and fungicides affected microbes the most. This study demonstrated that a scoring approach can be helpful in monitoring programs that aim to assess the risk of pesticides occurring in terrestrial ecosystems for environmental protection.

Graphical Abstract

Introduction

Pesticides (i.e., plant protection products – PPP) are intensively used in farming systems in Europe to secure crop yields and ensure food safety. From 2011–2020, an average of 350,000 tons of pesticides are used yearly in Europe. These pesticides constitute several thousand different commercial formulations of 455 approved active substances (A.S) . When applied in agriculture, pesticides tend to deposit on plant, soil, and water surfaces through direct spraying or wind drift and subsequent deposition. As a result, non-target organisms living in these environmental media can be exposed to pesticides. The exposure of non-target species to pesticides often leads to deleterious effects such as reproduction or growth inhibition, behavioural impairment, and in many cases, mortality. The toxic effect of pesticides depends on the dose that the organisms are exposed to, and the potency and toxic mode of action affecting distinct taxonomic groups differently. Sublethal effects of pesticides can be due to the low concentration of pesticides relative to the lethal effect. One major driver for exposure is the environmental persistence of the pesticide. The persistence of a pesticide is the measure of how long the pesticide can stay active and/or intact. In many cases, the pesticides could be transformed into metabolites that can be persistent and, in some cases, more toxic. For the currently approved substances in the EU, as part of the continuous assessment of their safety in the environment, it is pertinent to know if the concentrations present in the environment lead to acceptable risks. Since pesticides often exist as mixtures in the environment, their safety based on mixtures needs to be accounted for.

Documentary evidence showed that when organisms are exposed to chemical mixtures, they often elicit stronger ecotoxicological effects (due to additivity and/or potentiation) than when exposed to single chemicals. Ecotoxicological effects of mixtures can be observed even at concentrations safe for each single chemical exposure. In real agricultural soils, pesticides rarely occur as single substances but often together. Of 317 EU agricultural soil samples taken in the LUCAS monitoring campaign in 2015 across Europe, 83 % had pesticide residues, and 58 % contained pesticide mixtures. This is because i) in several pesticide formulations, more than one A.S. can be present, ii) for some applications, mixing of multiple PPPs can be recommended (tank mix), iii) pesticides can co-occur in the environment due to application of spray series schemes, iv) pesticides co-occur in the environment due to their re-distribution, persistence, and transformation. Therefore, organisms in the environment are potentially exposed to these mixtures. According to the EU Commission on Assessment of Mixtures, many studies have reported that few pesticides found in mixtures (priority pesticides) drive the majority of toxicity potency of the respective mixtures. Therefore, ecotoxicological tests do not need to be carried out with all the pesticides in the mixtures; instead, they should primarily focus on priority pesticides in the mixture that drive the overall toxicity of the mixture.

The persistence of a pesticide is an important characteristic that is often considered in environmental risk assessment. Some authors have argued that high persistence alone can be sufficient to trigger risk mitigation. Based on Knuth et al., the persistence of pesticides has been underestimated, where about 79 % of detected residues during soil sampling were from pesticides that were not applied in that growing season. Therefore, apart from the relative toxicity of the pesticides, persistence should be considered an essential criterion for cumulative mixture risk assessment. Since not all components of a mixture drive the toxicity, this study aims to elaborate a selection procedure for priority pesticides that potentially drive mixture toxicity in ecological receptors (fauna, flora, and microbes) in terrestrial compartments. The aim of this prioritization is to select the most relevant pesticide mixtures in 11 crop systems, which should be further assessed in ecotoxicological studies for risk assessment of the mixtures on the terrestrial ecosystem. To do this, we selected the pesticides by using the risk quotient of the pesticides, their persistence in the environment, and their frequency of detection as criteria for scoring and attributing equal weight of scoring to the criteria.

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