Accumulation and elimination of cyanobacterial hepatotoxins by the freshwater clam Anodonta grandis simpsoniana

Abstract

Freshwater clams (Anodonta grandis simpsoniana) exposed to 51-55 µg · L-1 of dissolved microcystin-LR (MC-LR) in the laboratory for 3 days did not accumulate MC-LR equivalents (MC-LReq). However, clams placed in three eutrophic lakes with phytoplankton containing MC-LR (concentrations from below detection to 8.3 µg · L-1 cellular toxin) for 12-28 days accumulated the toxin (24 ± 7 to 527 ± 330 ng · g-1 MC-LReq; mean ± SE). The relative MC-LReq concentrations in clams reflected MC-LR concentrations in lake phytoplankton, but individual variation was high. In individual clams exposed for 24 days, the average MC-LReq concentration was usually greater in the visceral mass than in gills and muscle, but average toxin concentrations in the three tissues were similar (587, 310, and 364 ng · g dry weight-1). In clams removed from the lake and placed in toxin-free water, MC-LReq concentrations in tissues declined rapidly for 6 days (by 69-88%) but remained relatively stable for the remaining 15 days. Analysis of clam tissues appears to be a more sensitive MC-LR indicator than analysis of phytoplankton. Accumulation of potent cyanobacterial toxins by this clam warrants further study as many are consumed by muskrats (Ondatra zibethicus), which in turn are consumed by terrestrial predators.

Spatial and temporal variations of microcystins in hepatopancreas of a freshwater snail from Lake Taihu

“…Similarly, studies with the three species of gastropod (Lymnaea stagnalis, Helisoma trivolvis, and Physa gyrina) (Zurawell et al, 1999), three freshwater Unionid bivalves (A. Woodiana, C. plicata, and Unio dougiasiae) (Yokoyama and Park, 2002) indicated that the concentration of microcystins in the tissue of the invertebrates was correlated with the toxin in phytoplankton, but not with extracellular aqueous microcystins. Meanwhile, some studies with the freshwater clam, Anodonta grandis simpsoniana (Prepas et al, 1997), the blue mussel, Mytilus edulis (Novaczek et al, 1991), and the gastropods (Lance et al, 2006) pointed out that the primary routes of uptake of algal toxins are through diet, and to a lesser extent, via uptake of dissolved toxins. In the present study, PCCA indicates that among biological variables, Microcystis biomass showed closer positive relationships with intracellular and extracellular toxins content than with MCs content in snail hepatopancreas, suggesting that in addition to Microcystis, other factors (e.g., water temperature) also substantially affected the accumulation of MCs in snail hepatopancreas.…”

Cyanobacterial toxins in Canadian freshwaters: A review

“…These studies not only provided information on the depuration kinetics of MC, but also addressed the question of whether toxin measured in clams and gastropods were due to direct accumulation of toxin from the surrounding water or exclusively to the presence of toxin-containing phytoplankton cells in the gastrointestinal tract. Prepas et al (1997) found that approximately 70% of MCs depurated from clams within the first 6 days of being transferred to clean laboratory aquaria. In addition, MC was not only found in the visceral mass (containing digested and undigested phytoplankton), but also in the gills and muscle tissue.…”

Fate of cyanobacterial toxins in the pelagic food web: transfer to copepods or to faecal pellets?

“…If the toxins are persistent, like microcystins (Lahti et al 1997), they may form a health risk via transfer and accumulation in the pelagic food web. In marine and freshwater ecosystems, the transfer of toxins has been suggested to occur via tintinnids (Maneiro et al 2000), copepods (White 1981, Teegarden & Cembella 1996, Tester et al 2000 or clams (Prepas et al 1997) to higher trophic levels such as fish, birds or baleen whales. Furthermore, herbivorous zooplankton, after ingesting toxic algae, may produce toxin-containing faecal pellets that either sediment or are consumed by other zooplankton in the water column (Maneiro et al 2000).…”