Environmental+Toxicology+Tox+2000+notes (2)

With appropriate treatment of effluents toxicity has

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Unformatted text preview: turned to pulp mill effluent receiving waters but now show a syndrome of symptoms related to effects on reproduction and induction of metabolic enzymes such as mi xed function oxidases (MFOs) in the liver. The MFO -related responses observed in these fish include increases in MFO activity and increased liver size (Munkittrick et al. 1992b, Munkittrick et al. 1994, Robinson et al. 1994) . Responses associated with reproductive effects include delayed age to maturity, decreased gonad size, decreased secondary sexual characteristics, smaller plasma steroid concentrations and reduced rates of steroid synthesis in the gonad ( Munkittrick et al. 1992a, Van der Kraak et al. 1992) . These responses have been observed at mills regardless of the use of primary or secondary treatment of effluents or chlorine bleaching of the pulp ( Munkittrick et al. 1994, Robinson et al. 1994), suggesting that these responses are caused by naturally produced organic compounds released from the wood during pulping and not from chlorinated substances that may be formed during bleaching. That endocrine modulating sub stances from natural sources can produce reproductive responses in fish is not surprising as they have been reported to cause effects in other organisms (Leopold et al. 1976). However, these natural substances are not thought o f as being persistent in the same sense as the organochlorine pesticides, such as DDT. Nevertheless, in the case of these natural substances, prolonged exposures do result from continuous release into the receiving environment. Even though these substances may be easily degraded and are nonbioaccumulative, their continuous presence in the environment can result in essentially the same exposure scenario as for persistent bioaccumulating substances as discussed above ( Figure 327). Thus, regardless of the cyclical nature of sens itivity, continuous presence of the substance ensures that responses will be observed. The exact identity of the substances in pulp mill effluent responsible for the reproductive responses or MFO induction is not known, however, retene type polyaromatic and chlorinated stilbenes have been implicated as possible MFO inducers (Parrott et al. 1995, Burnison et al. 1996) and phytosterols, such as β-sitosterol have been shown to produce some of the responses observed in fish in pulp mill receiving waters (MacLatchy and Van der Kraak 1995) . Condensates from the pulp production process have been reported to have effects on testosterone concentrations in exposed fish. These effects are not caused byphytosterols as these are not present in the condensates (Dubé and MacLatchy 2001). It has been shown that MFO induction in fish was short lived and returned to baseline activity in the absence of effluent exposure during a pulp mill s hutdown, showing that continuous exposures to the MFO inducers are required to maintain the observed response. Similar effects for the substances causing reproductive responses have not yet been observed. Analogous effects have been observed in fish exposed to sewa...
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