Environmental fate and ecotoxicological parameters differentiate between low-risk pesticides, candidates for substitution and conventional chemicals

The European Union (EU) promotes the use of plant protection products with lower environmental and human health risks. Low-risk active substances (LRAS) are proposed as alternatives to conventional synthetic chemical compounds (ScC) and substances considered candidates for substitution (CfS). However, we are still lacking solid science-based evidence for assigning pesticide compounds into these categories. We aimed to identify whether specific data used in environmental risk assessment can be used as effective descriptors of the three different pesticide categories. To achieve this, we conducted a meta-analysis based on environmental fate (DT50 soil and water/sediment) and ecotoxicological data (EC₅₀ and LC₅₀ values for algae, higher plant, aquatic invertebrate and fish) collected from peer-reviewed regulatory documentation of chemical pesticide active substances currently approved in the EU. Our meta-analysis showed that LRAS exhibited the shortest median DT50 values in soil (1.78 days) and water/sediment (7.23 days) and the highest median toxicity thresholds for aquatic organisms, particularly for P. subcapitata (EC50 = 10.3 mg/L) and L. gibba (EC50 = 100 mg/L), compared to ScC (DT50 19.74 days, EC50 1.094 mg/L and 1.1 mg/L) and CfS (DT50 80.93 days, EC50 0.147 mg/L and 0.154 mg/L). The latter showed significantly higher persistence and ecotoxicity from LRAS and ScC in most cases supporting the regulatory decision for withdrawal from the EU market. Overall ecotoxicological threshold values like EC50 values for algae and aquatic plants were good indicators distinguishing LRAS with conventional chemical compounds (ScC and CfS). Our findings constitute a first significant step that upon enrichment with more input data on LRAS, as more products from this group are coming in the market, and chronic ecotoxicity threshold values could establish a set of indicators that could support early-stage identification of new LRAS and extend to prioritize pesticide authorizations, streamline renewal or amendment procedures with reduced data requirements, and facilitate extension requests for existing approvals by focusing on LRAS.