Thus far, the best short-term study is by Brunel's Susan Jobling, who has shown that the threshold concentration of nonylphenol in water for vitellogenin production in male rainbow trout is approximately 10 µg/L, with inhibition of testicular growth at concentrations of >30 µg/L (13). The short-chain ethoxylates are likely to be similarly potent. Vitellogenin is a fish egg protein that is normally produced only in large amounts by female fish.
Jobling's study stands out because the fish were exposed to NP via the water, and then the concentrations were measured. The concentrations spanned the range reported in the environment. She also did full dose-response evaluations to substantiate her conclusions. These features make her study easier to interpret than the more numerous in vitro tests (14) that have measured the potency of APE biodegradation products.
Concerns about potential NP estrogenic activity emerged in 1991 when Ana Soto of Tufts Medical School observed that breast cancer cells, which normally proliferate only in the presence of an estrogen, exhibited the same response in plastic containers. Investigative work revealed that NP caused the growth.
These concerns grew when British researchers in 1994 found that male fish placed in cages near sewage treatment discharges produced large amounts of vitellogenin. APE metabolites were suspected to be responsible for these effects. However, natural and synthetic estrogens, not APE metabolites, have now been identified as the main estrogenic chemicals in that effluent (15). "APEs are still in the frame, at least in some situations," according to Sumpter. "But I think they are probably not the major culprits in many, perhaps most, effluents." - R.R.
