Feminisation of male clams Scrobicularia plana from estuaries in Southwest UK and its induction by endocrine-disrupting chemicals

Abstract

The risk of endocrine disruption in the marine environment is unclear and is often overlooked in invertebrates. We show that disruption to the 'normal' gonadal development of male estuarine clams Scrobicularia plana is occurring extensively at sites in Southwest UK, with populations exhibiting varying degrees of intersex (ovotestis). This is one of the few studies to have examined the extent of the condition in mollusc populations. Intersex was present in more than two-thirds of the populations screened from the Avon, Southampton Water, Bristol Channel/Severn, Erme, Plym, Fal, Tamar and Lynher Estuaries; severity varied, with between 0 and 60% of males exhibiting the condition. Prevalence of intersex tended to peak as gonads reached maturity in July, and was highest in clams from the Bristol Channel and Severn Estuary, coinciding with an increase in oocyte size in both the female gonad and in the ovotestis of affected males. Experimental exposures to sediment spiked with mixtures of 17β-oestradiol (E2), 17α-ethinyloestradiol (EE2), octylphenol (OP) and nonylphenol (NP) indicated that (xeno)estrogens could be a contributory factor in the induction of intersex and increased oocyte size. It is plausible, therefore, that the incidence of ovotestis may be linked to urban, industrial and agricultural influences, or a combination thereof, although the relative importance of these sources has yet to be determined. S. plana offers potential as a sentinel species for screening and investigation of endocrine disruption in the estuarine environment, helping to focus remediatory strategy where it would be most beneficial. © Inter-Research 2007.