Differential Bioaccumulation of Mercury and Selenium in Stomach Contents and Tissues of Three Colorado, USA, Cutthroat Trout Populations.

Total mercury (THg) and selenium (TSe) levels were measured in stomach contents (SC) and twelve tissues of cutthroat trout (Oncorhynchus clarkii) occurring in three high-elevation lakes of Colorado, USA, inhabiting watersheds absent past and current mining activities. For 32 of 36 tissues, including muscle, mean THg wet weight (ww) concentrations were greater than in the diet (SC) for all sites, indicating biomagnification. Ranges of THg (µg/kg ww) for SC and stomach tissue (ST) were 1.23-73.54 and 14.55-61.35, respectively. Selenium concentrations in fish muscle were not greater than in the SC indicating a trophic transfer factor < 1.0. However, in several other tissues, mean Se dry weight (dw) levels were greater than in SC for all three lakes. Ranges of TSe for SC and ST were 166-7544 and 797-7523 (µg/kg dw), respectively. The muscle to egg/ovary ratio for Se averaged 2.30, 4.60, and 2.68 for the three populations. The variability of SC (planktonic vs. benthic) and differential distributions of THg and TSe in SC and organ-tissues generated questions focusing on the seasonal, physiological, and genetic drivers of these organometal(loid)s in subalpine trout.

Effects of excess copper on growth of wild rice (Zizania palustris) seedlings tested in reconstituted and natural waters.

Dissolved copper was toxic to wild rice (Zizania palustris) seedlings when exposed in water from the seed collection site of Swamp Creek, Crandon, Wisconsin, USA, and in laboratory-prepared artificial or reconstituted water. Seeds for the study were harvested, then held through a portion of dormancy, in Swamp Creek. After 60 days they were shipped to a laboratory, chilled, and tested with copper after germination. The end point of the tests was net gain in wet weight of the seedlings; additionally, a pronounced reduction in root development was observed. Using measured concentrations, the lowest no-observable-effect concentration (NOEC) in our study was 37 microg/liter in Swamp Creek water and the lowest-observable-effect concentration (LOEC) was 59 microg/liter. However, it appeared that there was a point at which concentrations of copper above 400 microg/liter did not result in any measurable effect or exhibit a definitive dose-response. Because the results in Swamp Creek water were more relevant to the possibility of local metals additions and the association of reduced seedling growth by copper was more powerful in this water, we derived an equation to express the relationship between copper concentration and toxicity for Swamp Creek water. As an example, we would expect a 3.0% reduction in seedling growth at 5.0 microg/liter copper. Seedling roots were particularly affected and the resultant plants may be less well anchored and more susceptible to dislodging than plants not exposed to copper. Further refinement of the methodology may be used to address effects of other contaminants impacting rice beds in North America.