Estimated decline in global earthworm population size caused by pesticide residue in soil

Pesticides are potent chemical agents for protecting crops and agricultural production but can have secondary adverse effects on soil biodiversity that can propagate through all dimensions of soil security. Earthworms are among the most important actors in making soil healthy because they facilitate nutrient turnover, improve aeration, facilitate water infiltration into the root zone, and control soil-borne diseases. However, earthworms have been shown to be affected by the presence of pesticide residue, with a median survival to some highly toxic active substances concentrations as small as 4 mg/kg-soil. Here we have used the estimated pesticide residue of 87 active ingredients in nine different cropping systems globally, and we have developed the corresponding dose-response curve of earthworms to estimate the percent earthworm population decline and its global distribution caused by residues in the top soil. We found that vegetable and fruits, and orchards and grapes cropping systems are leading to the greatest percent decline in earthworms population in some areas of South America, and East and South East Asia. The decline in soybean, rice, and orchards and grape in boreal regions were the greatest. The maximum decline across the cropping systems ranged between 10 and 20% in about 1.2% of the agricultural locations under consideration, but it was less than 1% in about 66% of agricultural locations. These findings call for further scrutiny of the contamination by pesticide residue in soil and long-term consequences on soil security.