Page 977 - The Toxicology of Fishes

Case Study: Pulp and Paper Mill Impacts 957

Status of Identification of Responsible Chemicals

Despite the various approaches used to identify the bioactive compounds in PMEs, the compounds
responsible for the continuing reproductive changes in fish at some mills have remained elusive. The
initial uncertainty regarding the role of chlorine bleaching and dioxins in fish responses was resolved
by the mid-1990s, when it was determined that effects were not correlated with effluent adsorbable
organic halogen (AOX) levels and that releases of dioxins had decreased substantially (Munkittrick et
al., 1998; Owens, 1996; Sandström, 1995). In the mid-1990s, researchers were able to partially attribute
induction of detoxification enzymes in fish to wood components (Hewitt et al., 1996; Schnell et al.,
2000; Williams et al., 1996). Other studies, however, did not show direct correlation between indicators
of exposure (e.g., EROD activity) and primary wood components, such as resin acids (Ferguson et al.,
1993). Similarly, the observation that reproductive effects occurred in fish near mills with different
bleaching technologies suggested that the responsible compounds might be natural wood compounds as
opposed to cooking or bleaching chemicals (Hall and LaFleur, 2003; LaFleur and Barton, 2003; Van
Der Kraak et al., 1998). Some tannins, natural wood compounds that form the defense mechanism of a
tree to ward off insect infestations, and plant phytosterols are present in PMEs (Cook et al., 1997; Hall
and LaFleur, 2003; Van Der Kraak et al., 1998). Structurally, phytosterols have the potential to function
as hormone mimics affecting reproductive steroid production and function (Biermann, 1996). Some
studies showed that individual wood extractives (e.g., β-sitosterol) have the potential to affect fish
reproduction (Lehtinen et al., 1999; MacLatchy and Van Der Kraak, 1995; Van Der Kraak et al., 1998)
(Table 24.2); however, a lack of correlation between threshold reproductive responses and effluent
concentrations of individual wood species in effluents (e.g., plant sterols) suggested that additional
unidentified compounds and mechanisms were involved (Munkittrick et al., 1998). By the late 1990s,
source identification approaches, in concert with the development of mechanistically linked in vitro and
in vivo bioassays, have shown that multiple compounds in PMEs are affecting fish (Dubé and MacLatchy
2001; Hewitt et al., 2002; McMaster et al., 1996a; Van Der Kraak et al., 1992). Furthermore, it is highly
likely that the complexity of the responses is related to single chemicals exerting their effects in multiple
pathways, some of which are bound to interact with each other in the form of synergism and antagonism.
Thus far, accumulation studies have shown that bioactive substances are bioavailable and accumulated
rapidly, consistent with the body of evidence that has shown that a sustained exposure is required to
cause both elevated enzyme activity and depressions in sex steroid levels. The patterns of these substances
in effluents and fish tissues are not correlated with mill production type or effluent treatment. Collectively,
these findings show that bioactive substances originate from wood and are derived from lignin or
terpenoids. They are liberated during pulp digestion, and in kraft mills they are present in black liquor
and chemical recovery condensates (Dubé and MacLatchy, 2000a,b, 2001; Hewitt et al., 2005c; Martel
et al., 1997; Schnell et al., 2000). Additional bioactive substances are also present in bleachery effluents
containing residual lignin. Certainly, research in this area over the next decade will bring us closer than
ever to understanding why fish continue to be affected by PMEs and identifying the compounds
responsible for the effects.

Decision Making Relative to Pulp Mill Impacts
One of the greatest challenges in the next decade will be incorporating the science of PME effects
assessment into decision-making frameworks for stakeholders to assess how important an effect is, once
it is measured, and in the context of socioeconomic factors. With respect to the pulp and paper sector,
it has been difficult to obtain consensus among multistakeholder groups on definitions of what constitutes
an effect, when a response is an impact, and when an impact becomes damage. As an example, after 12
years of studies conducted on the potential impacts of PMEs at Jackfish Bay, Lake Superior, Ontario
(Munkittrick et al., 1998), there is no consensus on whether impacts exist. The controversy rests on
whether the delayed maturity and altered gonadal sizes observed at this site represent impacts. This lack
of consensus is not unique to PME effects assessment and has been observed for many different
anthropogenic stressors; however, the pulp and paper sector is in a unique situation. Due to the extensive