Are Clouds a Neglected Reservoir of Pesticides?

Pesticide contamination is a growing and alarming concern for both the environment and human health. Widely used in agriculture to control pests and disease carriers, pesticides undergo extensive long-range atmospheric transport in the gas phase, in aerosols, and, as shown here, in clouds. We measured the concentration of 32 pesticides at the puy de Dôme observatory (France) in the sub μg L^-1 to μg L^-1 range in cloud water, largely arising from regional to long-range transport that also involves pesticides currently banned for agricultural use in France. Half of the samples showed a total concentration of pesticides of over 0.5 μg L^-1, which is the European drinking water limit. If 2,4-dinitrophenol, which can also be produced by photochemical reactions, is excluded, two samples still present a total concentration of over 0.5 μg L^-1. The frequent detection of pesticides in rainwater may thus depend on their presence in clouds as well as atmospheric washout. Estimates of pesticides' quantity in clouds over France, ranging from 6.4 ± 3.2 to 139 ± 75 tons, suggest that their amounts in the cloud aqueous phase are potentially high and that these compounds would affect areas that are not directly impacted by agricultural activities.