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2011). Thus,harmful effects to predatory fish from mercury are not isolated to this action area, <br /> but are part of a geographically widespread problem. These studies indicate that while harmful <br /> effects may begin to be measurable in individual fish with concentrations of 0.5 µg/g WW in <br /> muscle tissue, or possibly less, some adult fish can persist with muscle tissue concentrations <br /> exceeding 1.0 µg/g (WW) (Sandheinrich and Wiener 2011). At these levels they would <br /> presumably be exhibiting sub-lethal effects, such as those described below. <br /> The harmful effects of methylmercury on fish populations at existing exposure levels in many <br /> North American freshwaters would be sub-lethal, such as cellular damage, reduced vigor, and <br /> reduced reproduction. Direct mortality due to methylmercury has been observed only at high <br /> concentrations (6-20 µg/g WW in muscle) (Sandheinrich and Wiener 2011). <br /> Rather than direct mortality, we expect that chronic toxicity from exposure to mercury in the <br /> action area may be affecting the endangered fish, as discussed below. Chronic toxicity is the <br /> development of negative effects as the result of long term exposure to a toxicant or other <br /> stressor. It can manifest as direct lethality but more commonly refers to sub-lethal endpoints <br /> such as decreased growth, reduced reproduction, or behavioral changes such as impacted <br /> swimming performance. <br /> Data from the Colorado Department of Public Health and Environment, Water Quality Control <br /> Division maintains a list of all waters in Colorado that exceed the total maximum daily loads for <br /> a variety of contaminants (CDPHE 2012b). Maintenance of this list is in accordance with <br /> Section 303(d) of the Federal Clean Water Act. The Water Quality Control Division does not <br /> list the Yampa or White Rivers as impaired for mercury levels. It should be noted, however, that <br /> impairment under this program relates to risk to humans and not necessarily to risk to aquatic <br /> species. <br /> As stated above,we know that the combustion of coal from the Trapper Mine at the Craig <br /> Generating Station is releasing mercury into the air and we have an estimate of this quantity. We <br /> do not know specifically, however,what proportion of that mercury deposits within the action <br /> area, the greater Yampa or White River watersheds, or is transported to distant locations beyond <br /> the limits of the local watersheds, although we have made a reasonable assumption of this <br /> amount. <br /> Although not fully understood or quantified, we believe the primary impact from coal <br /> combustion to the Colorado River fish is from the emission and subsequent deposition of <br /> mercury and eventual integration into fish tissue. Mercury poses a greater threat to the Colorado <br /> pikeminnow, as compared to the other endangered fish in the action area, and a greater threat <br /> than selenium,which is discussed below. Mercury has no beneficial use at any concentration for <br /> vertebrates and is considered toxic at much lower tissue concentrations than selenium. The <br /> chronic aquatic life standard for mercury concentrations in water is more than two orders of <br /> magnitude smaller than that for selenium. In most endangered fish tissue samples analyzed from <br /> the action area, mercury was close to or somewhat above the more conservative safe tissue level <br /> presented by Beckvar et al. (2005) and some also above the higher risk threshold presented by <br /> Sandheinrich and Wiener(2011). As discussed below, selenium tissue concentrations tested in <br /> the action area have ranged from levels indicating a minimal hazard to those indicative of a high <br /> hazard. <br /> 51 <br />