Formononetin from red clover – is freshwater fish at risk?
Pastures or grasslands with red clover produce tens to hundreds of kg per year of estrogenic isoflavones such as formononetin. Their potential entrance into the aquatic environment may pose a risk to aquatic organisms
Red clover (Trifolium pratense) contains 1 to 10 g/kgdw of formononetin. Its estrogenicity has been known since the 1940s, when sheep grazing on clover pastures in Western Australia were hit with infertility. Conversely, red clover has various medical uses, e.g. alleviation of menopausal symptoms.
While relatively hydrophobic in neutral form (log Kow = 3.1), the phenolic group deprotonates at circumneutral pH, which drastically increases aqueous solubility and mobility. Its half-life in natural waters is in the order of 40 days.
Formononetin is emitted from pasture via drainage water, in which it reaches concentrations in the low µg/L concentration range, leading to a continuous presence in connected surface waters at a few to a few 100 ng/L.
Consequently, in small rural river catchments without major anthropogenic activities, formononetin (and other isoflavones) may constitute a dominant and ecotoxicological relevant portion of the total estrogenicity. In contrast, its relevance in larger surface waters is probably small due to dilution.
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