Mollusk

Edible tissues of commercially important North American mollusks contained 

oysters, and mussels accumulate chromium from the medium or from contaminated sediments at comparatively low concentrations. For example, oysters subjected to 5.0 (xg Cr+ /L for 12 weeks contained 3.1 mg Cr/kg DW in soft parts and retained 52% of the accumulated chromium after they were transferred to chromium-free seawater for 28 weeks. Mussels (Mytilus edulis) subjected to the same dose-time regimen contained 4.8 mg/kg, but retained only 39% after 28 weeks of depuration. Both oysters and mussels contained higher residues after exposure to 10.0 jig Cr /L for 12 weeks 5.6 and 9.4 mg Cr/kg DW in soft parts, respectively, and both contained substantial (30-58%) residues after 28 weeks in a chromium-free environment. In studies with mussels and softshell clams (Mya arenaria), it was demonstrated that chromium in New Hampshire sediments (contaminated with Cr+ from tannery wastes) was bioavailable to clams by diffusion from seawater, and that both diffusion and particulate uptake were important pathways for mussels. Accumulation was observed at sediment chromium concentrations as low as 150.0 mg/kg. Kaolinite sediments containing up to 1200.0 mg Cr+ /kg produced the most pronounced adverse effects on filtration rates and ciliary activity of bivalve mollusks, leading the authors to conclude that chromium that has accumulated in areas affected by industrial wastes might have serious consequences to filter feeding bivalves. 

It is emphasized that Cr+, probably because of its very low solubility in seawater, appears to have a much lower bioavailability to most groups of marine animals than Cr+, which is more water soluble. The clam Rangia cuneata appears to be an exception it accumulated up to 19 mg Cr/kg in soft parts, on a dry weight basis, during exposure for 16 days to chromium-contaminated muds, and retained most of it for an extended period the estimated biological half-time was 11 days. In general, benthic invertebrates rarely accumulate chromium from contaminated sediments 

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For purposes of information one can compare these levels with those of plants (0.1 to 0.4%), mollusks (0.4%) and the human body (0.14%), but the highest levels are observed in marine algae (13% in Macrocytis pyrifera), and in the tissues of certain bacteria which can even contain elemental sulfur (25% in Beggiatoa Albea tissues). 

Thiazolopyridoacridine alkaloids obtained from marine sources, kuanoniamines (2a-c), bright yellow metabolites from the mollusk Chelynotus semperi, display... 

Schleim-tier, n. mollusk. -zellulose /. muco-cellulose. -zucker m. levulose. 

In contrast, jasplakinolide, a cyclodepsipeptide from the marine sponge Jaspis johnstoni, rapidly penetrates the cell membrane. It competes with phalloidin for F-actin binding and has a dissociation constant of approximately 15 nM. It induces actin polymerization and stabilizes pre-existing actin filaments. Dolastatin 11, a depsipeptide from the mollusk Dolabella auricu-laria, induces F-actin polymerization. Its binding site differs from that of phalloidin or jasplakinolide. 

FIGURE 19.15 A photomicrograph of the cross section of the mother-of-pearl lining a mollusk shell. The composite material making up mother-nf-pearl consists of flat crystals of calcium carbonate embedded in a tough, flexible organic matrix that resists cracking. 

FIGURE 19.16 The material used to make this high-performance car protects the driver by making use of a design like that of the mollusk shell in Fig. 19.15. The car is made of composite materials that are stronger than steel. 

The negative effects of TBT have been observed in the bivalve larval development of Crassostrea gigas, Mylilus edulisf Venus gallina, Spams aurata, in Nassarius reticulate and in the hermaphroditic snails Phisa fontinalis and Adelomelon brasiliana Since TBT exerts a variety of toxic actions on some mollusks and fishes , an adverse effect of TBT on human health is a real threat. ... 

Cause imposex in dog whelks and a variety of other effects on other mollusks... 

Warfarin, diphenacoum, bromodiolone, flocoumafen, and brodiphacoum are examples Both alkyl and aryl mercury compounds can bind to sulfhydryl groups Have caused population declines in certain mollusks... 

Most aquatic invertebrates have very little capacity for metabolism this is particularly true of mollusks. Crustaceans (e.g., crabs and lobsters) appear to have greater metabolic capability than mollusks (see Livingstone and Stegeman 1998 Walker and Livingstone 1992). 

Of particular interest in the present context is that TBT can inhibit cytochrome-P450-based aromatase activity in both vertebrates and aquatic invertebrates (Morcillo et al. 2004, Oberdorster and McClellan-Green 2002). The conversion of testosterone to estradiol is catalyzed by aromatase, and so inhibition of the enzyme can, in principle, lead to an increase in cellular levels of testosterone. The significance of this is that many mollusks experience endocrine disruption when exposed to TBTs,... 

Tributyltin compounds used as antifouling agents on boats have had serious toxic effects upon many mollusks, including populations of oysters and dog whelks. Females of the latter species developed a condition known as imposex, which rendered them infertile and caused local extinction of the population in shallow coastal waters. Imposex provides the basis for a valuable biomarker assay. 

PAHs can be bioconcentrated or bioaccumulated by certain aquatic invertebrates low in the food chain that lack the capacity for effective biotransformation (Walker and Livingstone 1992). Mollusks and Daphnia spp. are examples of organisms that readily bioconcentrate PAH. On the other hand, fish and other aquatic vertebrates readily biotransform PAH so, biomagnification does not extend up the food chain as it does in the case of persistent polychlorinated compounds. As noted earlier, P450-based monooxygenases are not well represented in mollusks and many other aquatic invertebrates (see Chapter 4, Section 4.2) so, this observation is not surprising. Oxidation catalyzed by P450 is the principal (perhaps the only) effective mechanism of primary metabolism of PAH. 

It appears that organisms at the top of aquatic food chains are not exposed to substantial levels of PAH in food because of the detoxifying capacity of organisms beneath them in the food chain. On the other hand, fish, birds, and aquatic mammals feeding on mollusks and other invertebrates are in a different position. Their food may contain substantial levels of PAH. Although they can achieve rapid metabolism of dietary PAH, it should be remembered that oxidative metabolism causes... 

Examples of differences in the responses of wildlife organisms to EDCs include the differences in sensitivity to phthalates and bisphenols among mollusks, crustaceans, and amphibians compared to fish. In invertebrates, biological effects are observed at exposures in the ng/L to low pg/L range, compared to high pg/L for most effects in fish (reviewed in Oehtmann et al. 2008). In addition, aquatic mollusks tend to bioconcentrate and bioaccumulate pollutants to a greater level than hsh, possibly owing to poorer capabilities for metabolic detoxification (see Chapter 4, Section 4.3). 

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