Reducing overall herbicide use may reduce risks to humans but increase toxic loads to honeybees, earthworms and birds

Background

Pesticide use has been associated with risks for human health and an overall decline in biodiversity. Although herbicides are the most commonly used pesticides worldwide, they have received less attention in this debate. We investigated the extent to which long-term trends in herbicide use in Austria influence potential toxic exposures to non-target organisms and potential risks to humans. We analyzed official sales data of 101 herbicide active ingredients (AIs) approved in Austria between 2010 and 2019 regarding their ecotoxicological properties based on lethal doses (LD₅₀ and LC₅₀) weighed by their persistence in the environment (DT₅₀) for honeybees (Apis mellifera), earthworms (Eisenia fetida), and birds (Serinus serinus). Human health risks were qualitatively assessed based on official hazard statements for the AIs used.

Results

In Austria, herbicide amounts sold decreased significantly by 24% from 1480 to 1123 tonnes between 2010 and 2019. This also led to a considerable decrease in the amounts of AIs classified by H-statements of the EU Pesticides Database: − 71% acute inhalation toxicity, − 58% reproductive toxicity,− 47% specific target organ toxicity. Yet, 36% of herbicides used were still classified as highly hazardous pesticides according to the Pesticide Action Network. Surprisingly, over the same period, toxic loads to honeybees increased by 487% (oral exposure), while lethal toxic loads to earthworms increased by 498%, and to birds by 580%. This can be attributed to a shift toward the use of more acutely toxic and especially more persistent AIs. The most problematic AI for honeybees, earthworms, birds and humans was the highly persistent diquat. The further ranking of the most toxic herbicides varied considerably depending on the organism. It is important to note that this toxic load assessment, like official environmental risk assessments, evaluates the potential risk but not the actual fatalities or real-world exposure.

Conclusions

Our results show a trade-off between herbicide amounts and toxicological hazards to humans and other non-target organisms. These interdependencies need to be considered when implementing pesticide reduction targets to protect public health and biodiversity, such as the EU´s “farm-to-fork” strategy, which aims to reduce the amounts and risks of synthetic pesticides.