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Penethyl isothiocyanate (PEITC) potentially is leaching into water courses and researchers are concerned the toxin can kill trout embryos and cause deformities.

, from the university’s Centre for Aquatic Environments, led the research which has been .

He said: “Results show the need to accurately quantify and monitor environmental levels of PEITC in the environment.”

Dr Crooks, with Asa White, a PhD student, and Centre colleagues Dr Angelo Pernetta and Professor Chris Joyce, Professor of Ecology, looked into the sources of PEITC.

Plants from the mustard or cabbage-family have evolved a chemical defence when chewed by grazing animals, a system called glucosinolate–myrosinase. It produces PEITC which acts as a deterrent to grazing invertebrates and can be toxic.

Left to right Dr Neil Crooks and Dr Angelo Pernetta

Asa White

PEITC can also be released into waterbodies including chalk-stream spawning sites of brown trout when plant matter containing active compounds is introduced to control soil-borne pests and diseases.

And, researchers discovered, it can also be released when watercress is harvested and washed.

The researchers exposed 1 microgram of PEITC to developing trout embryos and all died after four dose days; 0.1 microgram produced a four-fold increase in mortality than usual and a delay in hatching, lighter and shorter fish and deformities, while 0.01 micrograms had a negligible effect.

The study also revealed that newly-spawned trout which are exposed to PEITC showed a “significant decrease in swimming activity”.

Dr Crooks said: “Our research showed that damage caused by relatively low doses of PEITC highlights the need to closely watch and examine this environment. We need to gauge more precisely the level of PEITC being released into our rivers in order to get a better understanding of any damage being caused.”