The 96-h median lethal concentrations of nitrite to channel catfish (Ictalurus punctatus), tilapia (Tilapia aurea), and largemouth bass (Micropterus salmoides) under similar water quality conditions were 7.1 ± 1.9, 16.2 ± 2.3, and 140.2 ± 8.1 mg NO2-N/L (mean ± SE), respectively (pH 7.7–8.2; temperature 23 °C). During 24-h sublethal exposures to nitrite, methemoglobin concentrations in the blood of all three species generally increased with increasing nitrite concentrations. Channel catfish and tilapia concentrated nitrite in their blood above environmental levels and generated higher methemoglobin concentrations than largemouth bass at all nitrite concentrations tested. Largemouth bass did not develop elevated methemoglobin concentrations until NO2-N concentrations reached 48.7 mg/L, and plasma nitrite concentrations in largemouth bass were never observed higher than environmental concentrations. These data indicate that differences in resistance to nitrite among species may be partially due to a differential ability of some species to prevent the concentration of nitrite in the plasma.

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Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were measured in sediment, catfish, and crab tissue from 45 locations in the Houston Ship Channel in Texas in the Summer of 2002. Concentrations of individual 2378-substituted congeners ranged from 0. 1 to 42,000 ng/kg dry wt, from 0. 1 to 230 ng/kg wet wt, and from 0.1 to 260 ng/kg wet wt fo r sediment, catfish, and crab samples, respectively. OCDD concentrations in sediments were up to two orders of magnitude higher than those for the remaining congeners, but this signature was not observed in catfish and crab samples. Results from this study suggest that despite regulatory controls on discharges from pulp and paper mills, there has been little change over the last 10 years in dioxin concentrations in sediment and tissue from the Houston Ship Channel. Ongoing PCDD/PCDF inputs from urban and industrial areas along the channel as well as resuspension/desorption fro m contami nated sediments may provide a partial explanation for the lack of change. Simple correlation statistical and principal component analyses were undertaken.

Elevated but variable levels of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/Fs) were observed in hardhead sea catfish (HH) and blue crabs (BCs), as well as in water and sediment, of the Houston Ship Channel system, Texas, USA. It is hypothesized that the variation was caused by the spatial variability of PCDD/F contamination, together with the natural mobility of organisms in satisfying prey, temperature, salinity, and reproductive requirements. Structural equation modeling was applied to explore the congener-specific relationships between PCDD/F levels in HH and BC tissues and independent predictors such as PCDD/F contamination levels, environmental factors such as salinity and temperature, temporal-spatial factors such as site depth and season, and biological factors such as length, weight, and lipid content. Contamination levels in both sediment and water were statistically significant predictors of the levels of less chlorinated congeners in both HH and BCs, with the standardized regression weight for sediment concentration roughly twice that for the water concentration. This implies that sediments are the dominant route for PCDDIF exposure and remediation efforts should focus on legacy sediment ontamination. Tissue lipid content was a significant predictor of tissue concentrations in HH but only to a lesser extent in BCs, perhaps due to their low lipid content. Site depth and seasonal factors also were significant predictors of tissue concentrations. For the highly chlorinated congeners, only a small fraction of the variance in tissue concentrations was explained by the independent predictors, possibly indicating that uptake and elimination kinetics, biotransformation processes, or both may be more important factors controlling the bioaccumulation of those congeners.