Search

Antibiotic resistance genes (ARGs) are found in marine as well as terrestrial bacteria. Bivalves are known to accumulate chemical pollutants and pathogenic microbes, however, the fate of ARGs in bivalves after the intake of ARG-possessing bacteria is not known. Here we show that the copy number of oxytetracycline resistance gene tet (M) increased rapidly in the clam digestive tract by filtering water, then remained constant over 96 h in a tank experiment even with the addition of tet (M)-possessing bacteria every 24 h. >99.9% of the added tet (M) was decomposed, reaching a balanced state. Environmental sampling of mussel digestive tract and seawater supported the hypothesis that tet (M) was decomposed in bivalves as tet (M) was present in seawater from April to October at a concentration of 10 −5 to 10 −6 copies/16S, whereas tet (M) in mussels was mostly below the detection limit. Two (April) and three (July and October) individual mussels were positive for tet (M) with a concentration equivalent to that of seawater. We therefore conclude that bivalves do not accumulate tet (M) from seawater. [ABSTRACT FROM AUTHOR]

A series of laboratory experiments was conducted under realistic environmental conditions to test the ability of the Diffusive Gradient in Thin film (DGT) technique to mimic monomethylmercury (MMHg) bioaccumulation by a clam (Macoma balthica, Baltic clam). Using isotope enriched MMHg as tracers, bioavailability was determined by comparing the rate of MMHg uptake by novel DGT devices and sentinel organism over time. Experiments were conducted under varying conditions of salinity and MMHg speciation. Depending on MMHg level and speciation in the dissolved phase, MMHg uptake rates by the sentinel organism varied greatly from 0.4 to 2.4Lg−1 d−1. Reproducibilities of MMHg uptakes by DGT and clams were estimated at 7 and 38%, respectively. A significant linear relationship (log basis) between MMHg accumulation by DGT and clams was observed (r2 =0.89). The study demonstrates that DGT results reasonably predict MMHg uptake by clams from the aqueous phase and provide the basis for application of the DGT device as a surrogate for sentinel organism for monitoring bioavailable MMHg. [ABSTRACT FROM AUTHOR]

Abstract: Although metal contamination is a problem of major concern in the lagoon of New Caledonia due to intense mining activities conducted on land, very little is known on the metal ecotoxicology of local marine organisms. The clam Gafrarium tumidum was investigated to assess its usefulness as a bioindicator species of metal contamination in this lagoon. More particularly, allometric relationships between metal accumulation and clam size were determined for five common metals in New Caledonian lagoon waters (Cd, Cr, Co, Zn and Ag) using a highly sensitive radiotracer technique. Experimental results showed that allometric relationships were dependent on the element and on the body compartment considered. As a rule, allometric relationships of metal concentration factor were more pronounced in shell than in soft parts. Significant relationships with clam size for Cd, Cr, Co and Zn followed inverse power functions. In contrast, the degree of Ag bioaccumulation was positively correlated with size. In view of the literature on Ag in bivalves, the latter observation suggests the occurrence of a specific detoxification mechanism (sequestration) that would be more efficient in old individuals. Overall, the experimental results indicate that the use of G. tumidum as a bioindicator in monitoring programmes requires selecting individuals of a specific size range in order to obtain comparable information about ambient metal levels. Since the size effect is greatest among smaller individuals, it is recommended to select clams with a shell width greater than 35 mm. [Copyright &y& Elsevier]

Nowadays, several digestion protocols have been employed to extract microplastics from marine biota. However, the appropriate protocol and its optimal operating conditions to eliminate the clam Mactra veneriformis tissues have never been investigated. In this study, two synchronous phases were taken to select the compromise elimination protocol which was efficient in digesting biological materials with little effect on identification of the tested plastic polymers. Furthermore, the protocol from compromising results between two phases was optimized by an orthogonal experiment to determine the best operating conditions. Then, an application of the optimization protocol to investigate microplastics pollution in commercial clams was conducted. According to our results, 10% KOH showed fairly well digestion efficiency and little effect on identification of the tested microplastics. Furthermore, best operating conditions were demonstrated as treating clam tissues with 1:5 (M : V) of 10% KOH solution, incubating at 60 °C, shaking at 30 rpm for 12 h. In China, commercial clams were found contaminated with widespread microplastics pollution (3.50 ± 1.35 items/g). These problems should be further investigated and assessed due to the increased consumption as seafoods. Unlabelled Image • An optimization protocol of digesting clam Mactra veneriformis tissues. • 10% KOH is the compromise for extraction and identification of microplastics. • Incubating clams in 10% KOH with 1:5 (M : V) at 60 °C, 30 rpm, for 12 h was advised. • Microplastic average abundance was 3.50 ± 1.35 items/g in Chinese commercial clams. [ABSTRACT FROM AUTHOR]