Summary

1. Aquatic invertebrate populations represent an important part of the UK’s biodiversity, they provide valuable ecosystem services, recycling organic matter and keeping rivers clean. In addition they provide essential food for fish and birds.
2. Neonicotinoids are widely used insecticides with three main applications in the UK, firstly as a seed coating for field crops, secondly as sprays for crops and domestic gardens, and thirdly as an externally applied arthropod parasite treatment for pets.
3. Neonicotinoids are water soluble, mobile and can persist for months or years; as a result they have been found polluting waterbodies around the world.
4. Mayflies, caddisflies, flies and beetles tend to be most sensitive to neonicotinoid pollution. In laboratory tests half of mayflies and caddisflies died when exposed to concentrations in the range 0.1–0.3 μg/L; at just 0.03 µg/L 10% of mayflies died. Sub-lethal effects on invertebrates have also been detected, including, changes in feeding rates, mobility, predation rates, reduced growth and reduced emergence at levels between 0.3 and 1.5 μg/L.
5. In field studies a reduced abundance of aquatic insects is apparent when Imidacloprid concentrations in water are above 1 or 2 μg/L, and large scale surveys in the Netherlands revealed sharp declines in aquatic invertebrate abundance between 0.013 and 0.067 μg/L, while 0.02 μg/L led to a 30% fall in bird numbers over ten years.
6. The recommended ecological thresholds for neonicotinoid water concentrations are 0.2 μg/L – short-term acute – and 0.035 μg/L – long-term chronic; above these levels aquatic ecology can be expected to be significantly damaged.
7. Under the EU Water Framework Directive substances on a Watch List are being monitored, the list includes five neonicotinoid insecticides.

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