Assessment of the physiological impact of endocrine disrupting chemicals on salmonid fish from selected sites in Scotland and Northern Ireland
- Recent research in the UK and elsewhere has demonstrated that industrial and domestic effluents may contain compounds of both natural and synthetic origin which are steroid estrogens, or mimic the activity of steroid estrogens. Although present in solution at very low concentrations the sensitivity of the endocrine system of animals to interference is such that these contaminants represent a potentially disruptive threat.
- A survey of gonadal structure in roach populations in English rivers revealed that a high proportion (25% – 60%) of male fish within the sampled populations displayed evidence of abnormal gonadal development in the form of ovarian tissue within the testes. These effects were most pronounced at sites where discharged effluents represented a high proportion of total flow in the river. The functional significance of these observations has yet to be established.
- Concerns have been raised regarding the possible susceptibility of valuable salmon and trout populations to endocrine disruptive processes. This report describes the results of a field-based investigation of indicators of estrogen exposure in salmonid fish exposed to potentially estrogenic effluent discharges at sites in Scotland and Northern Ireland.
- This study addressed the possibility that native salmonid populations are being exposed to estrogenic contaminants via both domestic and industrial discharges and that this exposure may result in inappropriate and possibly detrimental physiological effects in exposed fish.
- This objective was addressed by the sampling of brown trout and Atlantic salmon from sites receiving a STW discharge and from pristine sites. Blood levels of the estrogen-inducible yolk precursor vitellogenin were measured to assess whether there was evidence that the targeted populations were exposed to acute estrogen exposure. In addition, gonadal material sampled from each fish was examined microscopically for evidence of abnormal reproductive development, the presence of which would be indicative of early or possibly chronic exposure to estrogens.
- A total of 209 fish were examined from four sites in Scotland [R. Teviot, Slitrig Water (tributary of the R. Teviot), Wilson Burn and Ale Water (pristine sites)]. Fish sampled from the R. Teviot were removed downstream of the Hawick STW discharge. In all the fish which were sampled blood vitellogenin levels were low, displaying no evidence of environmental estrogen-induced elevation. The gonadal structure of all the sampled fish was normal, with no evidence of ovarian tissue in male testes and no evidence of unusual ovarian development in female fish.
- A total of 64 fish were examined from three sites in Northern Ireland (Minnowburn, Collin River and Ravernet River; all tributaries of the R. Lagan). As was the case for the Scottish sites, no evidence of gonadal abnormalities was obtained in fish from any site.
- In addition to the field sampling, the estrogenicity of the effluents discharged at each site were evaluated by bioassay. In Northern Ireland, rainbow trout were held in cages submerged in the vicinity of the New Holland Sewage Treatment Works (STW) effluent discharge (R. Lagan). An aquarium-based exposure of rainbow trout to Hawick STW (R. Teviot) final effluent, at concentrations up to 100%, was employed. Analysis of blood vitellogenin levels after a period of or 11 – 14 days exposure in aquaria revealed that the Hawick STW effluent was not estrogenic. However, fish exposed to New Holland STW final effluent in situ for 3 weeks displayed elevated blood vitellogenin levels, relative to fish caged at control sites, indicating that the effluent contained estrogenic components.
- Water samples collected from both study sites were analysed for total alkylphenols and alkylphenol ethoxylates (APEs; ubiquitous environmental contaminants and known estrogen mimics found in high concentrations in English rivers with a high incidence of intersexuality). Samples from the Hawick sites contained very low levels of APEs (< 3 :g l-1). Similar levels were found in samples from the sites in Northern Ireland with the exception of effluent samples taken downstream of the Barbour Campbell Linen Mill which contained 12 :g l-1 total APEs. Steroids were not quantified in these samples.
- The microscopic examination of gonad structure, and analysis of blood vitellogenin levels, indicated that there was no evidence of exposure to estrogenic contaminants in the salmonid fish populations of the R. Teviot or R. Lagan.
- A number of factors probably contribute to this result. Salmonid fish exhibit a life-history very different to that of cyprinid fish such as roach in which effluent-related intersexuality has been reported. Trout and salmon normally spawn in clean gravel beds in the upper reaches of a river system and newly-hatched and early juvenile salmonid fish remain in these relatively pristine stretches of river. They are therefore not usually exposed to point-source effluent discharges during critical early developmental stages when the reproductive system is particularly sensitive to external influences. In addition, both salmon and migratory brown trout (sea trout) are anadromous fish, spending a significant proportion of their lives at sea. These factors contrast with the potential for life-long exposure to contaminants displayed by non-migratory cyprinid fish which spawn in the main body of the river. Additionally, salmonid fish are less tolerant of poor water quality than cyprinid fish and even the non-migratory brown trout are therefore not normally present in rivers subject to high effluent input. Most rivers which support populations of salmonid fish do not pass through heavily populated or industrialised areas. There is therefore less likelihood that these fish populations will encounter high concentrations of endocrine disrupting chemicals (EDCs).
- Overall, these data do not provide absolute reassurance that salmonid fish are unaffected by estrogens and estrogen mimics present in effluent discharges but they do indicate that if a problem does exist it may be localised and on a smaller scale than has been reported for cyprinid fish.
- Consideration should be given to a more widespread survey of gonad structure in salmonid fish populations in order to confirm these preliminary conclusions. It should also be considered whether reproductive performance of salmonid fish might be influenced by exposure to EDCs via mechanisms which do not involve alterations in gonadal structure (e.g. alterations in fecundity, gamete quality, behavioural changes). In addition, the possibility that aspects of the salmonid life-history other than reproductive development may be affected by EDCs should be examined.
- For example, smoltification (pre-migratory sea water adaptation) is a critically important aspect of the salmonid life history. Smoltification is closely regulated by the endocrine system and may be susceptible to interference by chemicals which mimic or interfere with the activity of hormones other than estrogens.
- It should also be considered whether sources of contamination other than effluent discharges (e.g. agricultural run-off) may expose salmonid fish to endocrine-disrupting chemicals.
Endocrine disruption, trout, salmon, reproduction, vitellogenin, gonadal structure, effluent, sewage, R. Tweed, R. Teviot, R. Lagan.
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