Oxygen uptake and nitrogenous excretion rates during overwinter degrowth conditions in the pulmonate snail, Helisoma trivolvis

Effects of Cd and Zn on oxygen consumption and ammonia excretion in sipuncula (Phascolosoma esculenta)

Physiological responses (oxygen consumption and ammonia excretion) of the sipuncula (Phascolosoma esculenta) exposed to four concentrations of Cd (0.45, 0.96, 2.04, and 4.46 mg L(-1)) and four concentrations of Zn (1.09, 2.34, 4.96, and 10.91 mg L(-1)) were monitored for 21 days, respectively. Oxygen consumption rates of sipuncula at all concentrations of Cd decreased from day 1 to day 6. At low concentrations of Cd (0.45 and 0.96 mg L(-1)), the oxygen consumption rate was promoted. Time and concentration were significant in affecting oxygen consumption rate, respectively. Oxygen consumption rate decreased significantly with time for Zn-exposed individuals and also decreased significantly with the interaction between the concentration of Cd and time for Cd-exposed individuals. Changes occurred in the ammonia excretion rates and O:N ratios with individual sipuncula experiencing different metal concentrations over time. Although low O:N ratios (<30) were obtained in most of the treatments, no predictable correlation was found between concentrations of metals and values of O:N obtained. The value of using O:N ratio as a stress index is questioned.

A review of the effects of heavy metals on freshwater mussels

: The widespread recent decline in the species diversity and population density of freshwater mussels in North America may be partly related to chronic, low-level exposure to toxic metals. As benthic filter-feeding organisms, freshwater mussels are exposed to metals that are dissolved in water, associated with suspended particles and deposited in bottom sediments. Thus, freshwater mussels can bioaccumulate certain metals to concentrations that greatly exceed those dissolved in water. In adult mussels, the most common site of metal uptake is the gill, followed by the mantle and the kidney. The toxic effects of metals on freshwater mussels have been examined in a few acute toxicity tests, but the sublethal effects of long-term exposure to low environmental concentrations are little understood. Sublethal exposure to metals can alter growth, filtration efficiency, enzyme activity and behaviour. Sublethal effects are frequently observed at concentrations that are only half the lethal concentrations. However, few toxicity tests have used environmentally realistic exposure concentrations. Total concentrations of Cd, Cu, Hg and Zn in many oxic surface waters are in the ngl(-1) range, yet many toxicity studies have exposed mussels to concentrations in the μgl(-1) or even the mgl(-1) range. An understanding of the processes by which metals affect freshwater mussels would provide insights on the ecotoxicological significance of metal contamination to natural mussel populations and aid in the development of water-quality criteria that adequately protect mussels.

The effects of intermittent exposure to suspended solids and turbulence on three species of freshwater mussels

A laboratory experiment was performed to evaluate the effects of intermittent suspended solids exposure on the unionid clams Quadrula pustolosa, Fusconaia cerina and Pleurobema beadleanum. Intermittent impacts of this type are important effects of commercial navigation traffic in freshwater. Clams were cyclically exposed to turbulence alone or accompanied by 600-750 mg litre(-1) of suspended inorganic solids for 9 days. Clams exposed to suspended solids every 3 h reduced their metabolic rate but did not shift from the mainly protein based catabolism of controls. Feeding impairment was apparently compensated for by a reduction in metabolic demand. Conversely, clams exposed every 0.5 h to suspended solids shifted to virtually complete reliance on non-protein body stores as indicated by O:N values averaging 197.