The adsorption-desorption behavior and bioavailability of mercury and cadmium in a model salt marsh ecosystem have been investigated. Specimens of two species of filter-feeding mussels, Mytilus edulis and Modiolus demissus, were placed in large rectangular enclosures containing marsh peat previously equilibrated with a seawater solution of the metals. The tissue concentration was determined after 21 and 70 days. Correlation between the levels of these metals in mussel tissue and the following parameters were examined: percent total organic matter, sediment metal concentration, acid leachable metal concentration, and amounts of metal desorbed from the sediment. Multiple regression analysis indicated a strong dependence of sorption-desorption processes on sediment organic matter content for both metals. Uptake of mercury was found to depend primarily on the amounts of acid leachable metal and the amounts of metal desorbed from the sediment. Cadmium uptake depended primarily on percent total sedimentary organic matter and the amounts of metal desorbed.
The planktonic diatom Skeletonema costatum was exposed during 4-h periods to dissolved forms of H2S and CO2. The experimental design permitted evaluation of the acute toxicity of these gases by measuring the reduction in photosynthesis using the 14C assimilation technique. Carbon dioxide gas, measured with a CO2-specific electrode, demonstrated a EC50 value of 0.69-mM molecular CO2. The inhibition in algal photosynthesis was largely attributed to the decrease in pH with increasing exposure concentrations (from pH 8.45 to 5.73). Hydrogen sulfide, measured colorimetrically, showed no adverse effects up to 24-μM total sulfide corresponding with 1.2-μM molecular H2S. The calculated EC50 value was 3.1-μM H2S. The toxicity tests yielded results useful for the assessment of potential harmful effects to marine diatoms of discharge of these gases into ocean waters by off-shore natural gas production platforms.
A series of static and flow-through toxicity tests was conducted to determine the toxicity of drilling mud that contained three classes of hydrocarbon additives-low-sulfur diesel fuel, high-sulfur diesel fuel, or a commercial mineral oil additive-to four species of marine invertebrates. The hydrocarbon additives were chemically characterized by computerized gas chromatography/mass spectrometry. The base mud was a laboratory-formulated freshwater lignosulfonate mud (generic mud No. 8). Acute toxicity tests were performed with mysids (Mysidopsis bahia) by using the suspended particulate phase (SPP) of a 1 : 9 dilution of drilling mud with seawater. Ten-day solid phase (SP) toxicity tests were conducted with sand worms (Nereis virens). grass shrimp (Palaemonetes pugio), and soft-shell clams (Mya arenaria) by using mud solids that settled to the bottom of the mixing container during a 1-h settling period. Exposure concentrations of total hydrocarbons, biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total organic carbon (TOC) were confirmed analytically. Base mud without additives was practically nontoxic. Drilling mud that contained 5% mineral oil was less toxic than mud containing 5% of either low- or high-sulfur diesel fuel additive, with LC50 values of 3090, 451, and 276 mg/L, respectively. Drilling mud solids containing mineral oil were not acutely toxic to the test organisms, but lethality was observed when animals were exposed to the mud solids that contained 5% diesel fuel.
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