Domoic acid contamination within eight representative species from the benthic food web of Monterey Bay, California, USA

Benthic food webs often derive a significant fraction of their nutrient inputs from phytoplankton in the overlying waters. If the phytoplankton include harmful algal species like Pseudo-nitzschia australis, a diatom capable of producing the neurotoxin domoic acid (DA), the benthic food web can become a depository for phycotoxins. We tested the general hypothesis that DA contaminates benthic organisms during local blooms of P. australis, a widespread toxin producer along the US west coast. To test for trophic transfer and uptake of DA into the benthic food web, we sampled 8 benthic species comprising 4 feeding groups: filter feeders (Emerita analoga and Urechis caupo); a predator (Citharichthys sordidus); scavengers (Nassarius fossatus and Pagurus samuelis) and deposit feeders (Neotrypaea californiensis, Dendraster excentricus and Olivella biplicata). Sampling occurred before, during and after blooms of P. australis in Monterey Bay, CA, USA during 2000 and 2001. DA was detected in all 8 species, with contamination persisting over variable time scales. Maximum DA levels in N. fossatus (674 ppm), E. analoga (278 ppm), C. sordidus (515 ppm), N. californiensis (145 ppm), P. samuelis (56 ppm), D. excentricus (15 ppm) and O. biplicata (3 ppm) coincided with P. australis blooms, while DA levels in U. caupo remained above 200 ppm (max. = 751 ppm) throughout the study period. DA in 6 species exceeded levels thought to be safe for higher level consumers (i.e. ≥20 ppm) and thus is likely to have deleterious effects on marine birds, sea lions and the endangered California sea otter, known to prey upon these benthic species.

Immunomodulatory effects of domoic acid differ between In vivo and In vitro exposure in mice

The immunotoxic potential of domoic acid (DA), a well-characterized neurotoxin, has not been fully investigated. Phagocytosis and lymphocyte proliferation were evaluated following in vitro and in vivo exposure to assay direct vs indirect effects. Mice were injected intraperitoneally with a single dose of DA (2.5 µg/g b.w.) and sampled after 12, 24, or 48 hr. In a separate experiment, leukocytes and splenocytes were exposed in vitro to 0, 1, 10, or 100 µM DA. In vivo exposure resulted in a significant increase in monocyte phagocytosis (12-hr), a significant decrease in neutrophil phagocytosis (24-hr), a significant decrease in monocyte phagocytosis (48-hr), and a significant reduction in T-cell mitogen-induced lymphocyte proliferation (24-hr). In vitro exposure significantly reduced neutrophil and monocyte phagocytosis at 1 µM. B- and T-cell mitogen-induced lymphocyte proliferation were both significantly increased at 1 and 10 µM, and significantly decreased at 100 µM. Differences between in vitro and in vivo results suggest that DA may exert its immunotoxic effects both directly and indirectly. Modulation of cytosolic calcium suggests that DA exerts its effects through ionotropic glutamate subtype surface receptors at least on monocytes. This study is the first to identify DA as an immunotoxic chemical in a mammalian species.