Multiple pesticides in lentic small water bodies: Exposure, ecotoxicological risk, and contamination origin

Lentic small water bodies (LSWB) are a highly valuable landscape element with important ecosystem services and benefits for humans and the environment. However, data about their pesticide contamination dynamic and the associated ecotoxicological effects are scarce. To overcome these knowledge gaps, five LSWBs located in agricultural fields in Northern Germany were studied during the spring pesticide application period (April to July 2018) and the concentrations of 94 pesticides were measured in weekly intervals. The goals of this study were to observe the trends of pesticide contamination during the application period, assess the ecotoxicity of the contamination, and assign the findings to temporal and spatial origins. Samples contained pesticide concentrations between 0.12 and 4.83 μg L−1 as sums. High detection frequencies (81% of samples) and concentrations (max 1.2 μg L−1) were observed for metazachlor transformation products. Contamination from multiple pesticides was detected with up to 25 compounds per sample and a maximum of 37 compounds per LSWB during the entire sampling period. High toxicities for algae and macrophytes were recorded using toxic units (TU) of −0.2 to −3.5. TUs for invertebrates were generally lower than for algae/macrophytes (−2.7 to −5.2) but were also recorded at levels with ecological impacts. Pesticide detections were separated into four categories to assign them to different temporal and spatial origins. Pesticides from the spring (5–11%) and the previous autumn (0–36%) application periods were detected in the LSWB. Some pesticides could be related to the application of the previous crop on the same field (0–39%), but most of the compounds (44–85%) were not related to the crop management in the last two years on the respective LSWB fields. The relevance of different input pathways is still unknown. Particularly, the effect of long-distance transport needs to be clarified to protect aquatic biota in LSWBs.