Sammy M. Ray

Metal partitioning between colloidal and dissolved phases and its relation with bioavailability to American oysters

Kinetics and the extent of metal partitioning between colloidal and dissolved phases and coagulation of metals associated with colloids were examined to determine their effects on the bioavailability of selected metals (Cd, Co, Hg, Ag, Fe, and Zn) to American oysters (Crassostrea virginica) using radiotracer and short term exposure experiments. After dispersion of radiolabeled colloids into low molecular weight (LMW, < 1 kDa) seawater, metal partitioning between dissolved (<1 kDa) and colloidal (1 kDa-0.2 microm) phases resulted in a consistent pattern, with a relatively constant percentage in the colloidal phase for each metal. On average, about 90% of Hg and Fe, approximately 60% of Ag and approximately 40% of Zn, Co, and Cd were measured in the colloidal fraction during a short term exposure experiment, consistent with their partitioning in natural waters. Controlled laboratory experiments carried out in parallel using radioactively tagged colloids showed that coagulation of colloidal species, quantified as the fraction retained by a 0.2 microm filter, was insignificant for most metals under the conditions and time periods of the uptake experiments. The bioavailability of colloidally complexed metals, measured in terms of dry weight concentration factor (DCF, ml g(-1)) and uptake rate constant (ml g(-1) h(-1)), was somewhat depressed compared with their counterpart in the LMW treatment, but could be well predicted from the results of the LMW treatment and metal partitioning. Both DCF values and uptake rate constants were higher in the LMW treatment than in the colloidal treatment. In addition, B-type metals, such as Ag, Hg, and Zn, all had higher values of DCF and uptake rate constants, regardless of treatments, except for Cd which had a lower DCF and uptake rate constant. In contrast, Co and Fe had significantly lower DCF values and uptake rate constants. Most of Hg and Ag (60-80%) were measured in the soft tissue of oysters in both LMW and colloidal treatments. In contrast, 80% of Fe, 75% of Co, and approximately 60% of Cd were observed on the shell, while Zn was found evenly distributed between shell and soft tissue of oysters. These results agree well with the variation pattern of both DCF value and uptake rate constant for these two groups of metals.

Effects of various antibiotics on the fungus Dermocystidium marinum in thioglycollate cultures of oyster tissues

Abstract Twelve antifungal antibiotics were screened to determine their potential for controlling Dermocystidium marinum, a lethal fungus parasite of oysters. Two antibiotics, cycloheximide and streptimidone, completely inhibited enlargement of D. marinum in thioglycollate cultures at concentrations of 0.25–1.0 μg/ml. Cycloheximide shows promise for use in arresting D. marinum infections in oysters held in closed laboratory systems. Twenty-two antibacterial antibiotics were screened for their effect on the enlargement of D. marinum in thioglycollate cultures, and for their efficacy in retarding growth in bacteria associated with oyster tissues. Three tetracyclines (tetracycline, chlortetracycline, and oxytetracycline), bacitracin, and gramicidin showed effective antibacterial properties at levels of 250–500 units or mcg/ml. However, all of these agents except gramicidin markedly inhibited parasite enlargement at concentrations of 250–750 units or mcg/ml. Further studies proved gramicidin to be inferior to either chloramphenicol or the penicillin-dihydrostreptomycin combination for inhibiting bacterial growth and tissue putrefaction in the thioglycollate culture technique for detecting D. marinum.

Protective Role of Alginic Acid Against Metal Uptake by American Oyster (Crassostrea virginica)

Little is known about how colloidal macromolecular organic matter (COM) modifies the bioavailability of toxic metals to aquatic organisms. In order to understand the physical and chemical properties of COM on the bioavailability of some metals to estuarine bivalves used as biomonitors, American oysters (Crassostrea virginica) were exposed to natural COMs and model acid polysaccharides (APS, alginic acid (AA), kappa carrageenan (CAR), and latex particles), and natural colloidal organic carbon (COC), tagged with either radioactive Ag, Cd, Co, Cr, Fe, Hg or Zn, or 14 C-labelled sugar OH groups. Filter-feeding oysters efficiently removed latex particles 0.04 µm in diameter, with removal half-times of 2.5-5.5 h, equivalent to a filtration rate of approximately 3 L day −1 g −1 . Thus, AA protects against metal uptake by oysters, which is confirmed by metal dry-weight concentration factors (DCFs) similar to, or lower than, those for 14 C-labelled AA. However, metal-DCFs for CAR and COC were higher than for 14 C-labelled counterparts, suggesting that in these treatments, metal uptake was enhanced over that of carbon. The 14 C-labelled AA was taken up significantly more than other 14 C-labelled organics, suggesting different behavior in the digestive tract. Bioavailabilty of metals bound to organic nanoparticles with different nutritional and physiological properties is not fully understood, and will require further experiments.

Electrophysiological and biochemical characteristics of Gymnodinium breve toxins.

Abstract Five toxins (T1–T5) have been isolated from a crude acidified ether extract of unialgal cultures of the dinoflagellate Gymnodinium breve Davis using techniques of column, liquid and thin layer chromatography. Electrophysiological studies using the spontaneously active ventral nerve cord preparation of the crayfish showed that two of the fractions, T2 and T4 caused excitation to more than 250% of control levels at a concentration of 0·05 ng/ml. A blockage of firing occurred at higher concentrations. Fractions T1, T3 and T5 produced gradual excitation only at the higher concentrations. T2 and T4 at a concentration of 250 ng/ml also produced excitation and irregular firing in central neurons from Aplysia californica. Studies on the effect of purified toxins on total choline incorporation in C61A rat glia clone cultures indicate that toxins T2–T5 increase lipid vs nonlipid choline metabolites, presumably by base exchange stimulation. Only T2 stimulated choline uptake in this system.