An app that can evaluate pollution in watersheds could help reduce aquatic toxicity from the cultivation of almonds in California's agricultural regions.

The web-based tool developed by researchers at the University of California, Santa Barbara, quantifies the toxicity from pesticides experienced by aquatic organisms, including fish, invertebrates and plants. Digital mapping illustrates the applied toxicity of each watershed by active ingredient and location.

Pesticides are a leading source of chemical hazards in aquatic environments, but their use in California is dominated by a handful of crops, especially almonds and other nuts. California produces 80% of the world's almonds, which are the state's most valuable export crop.

Historically the possibility of reducing pesticide toxicity in watersheds has been limited by ability to quantify usage and toxicity of pesticides, along with impacts over spatial and temporal scales. To provide a framework to target the reduction of pesticide use, the authors developed the Environmental Release Tool (ERT), using watershed data from the US Geological Survey.

ERT is a web and desktop application that summarises pesticide applications and toxicity by watershed. The researchers used it to analyse pesticide use across 140 California watersheds receiving agricultural applications.

The tool could quantify the toxicity released to aquatic biological life across these watershed areas, representing some 20% of US pesticides, and covering hundreds of agricultural commodities. The researchers demonstrated that mitigation actions on just two pesticides and 16 site types would affect about 90% percent of applied toxicity to fish, aquatic invertebrates and plants in California’s agricultural landscapes.

The study also showed that 20% of agricultural watersheds account for 80% of applied toxicity, suggesting that targeting a small number of watersheds that receive high concentrations of pesticides could be effective in reducing overall chemical toxicity. The tool has some important limitations—for example, it does not predict risks to human health or watershed ecologies, only opportunities to decrease pesticide toxicity.

A study has been published in PLOS Water by researchers Nicol Parker and Arturo Keller, who say that as well as developing the ERT, they have proven that it can be a valuable tool for identifying the environmental toxicity of pesticides, and should be considered in future agricultural management strategies.

They add, "The applied toxicity of agricultural pesticides in California is dominated by a handful of pesticides, and a few crops like almonds and other nuts. Careful selection of less toxic pesticides for the same crops can drastically reduce overall applied toxicity in California, and probably around the world."