The UK environment watchdog is examining whether more than 50 sites that supply salad and vegetables to supermarkets and other businesses are discharging chemical pollution into rivers and streams, The Guardian reports.

The action follows revelations that a salad producer supplying retailers including Waitrose was washing pesticides into a protected chalk stream in Hampshire.

The Environment Agency (EA) took action against Bakkavor, which runs a watercress plant in Alresford, for discharging neonicotinoids into the Upper Itchen, a protected chalk stream, after evidence was gathered by the environmental charity Salmon & Trout Conservation (S&T).

Bakkavor imports salad crops from the US and Europe as well as growing its own produce. The produce is washed onsite and the company has a permit from the EA to discharge wastewater into the Upper Itchen.

Experts from S&T forced the agency to act on pollutants in the river after working with local people to carry out sampling of the water, which suggested chemicals were affecting invertebrate communities including freshwater shrimp, mayflies and caddisflies.

Freedom of information requests submitted by S&T revealed that acetamiprid, a neonicotinoid, was being washed off the salads into the river at concentrations above acceptable levels.