Reducing disease and producing food: Effects of 13 agrochemicals on snail biomass and human schistosomes

Agrochemical use is predicted to increase 2-5 fold by 2050 to meet food demand. Evidence suggests that agrochemical pollution could increase snails that transmit the disease schistosomiasis to 250 million people, but most agrochemicals remain unexamined. Here we quantify the relative effects of fertilizer, six insecticides, and six herbicides on snail genera responsible for 90% of global schistosomiasis cases. We identified fertilizers and 4 of 6 insecticides as high risk for increasing snail biomass by increasing snail resources (vegetative habitat and periphytic food) and reducing snail predators, respectively. Herbicides generally had negative effects on snails by reducing vegetative habitat, with two herbicides increasing snails in the absence of aquatic vegetation. Parasite production, which reflects human infection risk, scaled positively to snail biomass. Our findings suggest that fertilizers and insecticides are more likely to increase human schistosomiasis than herbicides and revealed several low risk agrochemicals that might increase crop production without increasing schistosomiasis.