Microcystin concentrations in cyanobacteria and their accumulation in rainbow trout (Oncorhynchus mykiss) and freshwater mussels (Hyridella menziesi) in Lakes Rotoiti and Rotoehu (New Zealand) were investigated. Hatchery rainbow trout were added to an enclosure in Lake Rotoiti where concentrations of microcystins in the phytoplankton and cyanobacterial cell concentrations could be closely monitored. Rainbow trout that were free to roam in the entire area of each lake were also included in the study. Freshwater mussels were suspended subsurface in cages in the enclosure. Phytoplankton samples, rainbow trout liver and muscle tissue, and the tissues of mussels were analyzed for microcystins using the ADDA-ELISA method, and selected samples were analyzed using LC-MS. A maximum concentration of microcystins in the phytoplankton samples of 760 microg L(-1) was recorded in Te Weta Bay, Lake Rotoiti, in March 2004. ELISA results confirmed microcystin immunoreactivity in rainbow trout liver and muscle tissues and in freshwater mussels. The microcystin congeners LR, YR, RR, AR, FR, LA, and WR were detected by LC-MS in caged freshwater mussels in Lake Rotoiti but were not detected in either muscle or liver tissue of rainbow trout. The daily tolerable intake limit of microcystins for human consumption recommended by the World Health Organisation is 0.04 microg kg(-1) day(-1). Modeling was carried out for the human intake of microcystin compounds from rainbow trout muscle tissue, and the potential health risks were estimated, assuming the ADDA-ELISA was determining compounds of toxicity equivalent to microcystin-LR.
A flow injection (FI) atomic fluorescence method incorporating an on-line bromide-bromate oxidation step to determine mercury in filtered sea-water samples at the ng 1-' level is described. A heated reaction coil was incorporated in the FI manifold to increase the conversion of organic mercury into inorganic mercury(n) chloride from 50 to approaching 100%. Detection limits (3a) for mercury(I1) chloride and methylmercury chloride were 25 and 23 ng I-' Hg, respectively. The FI manifold could also be used to determine the total mercury concentration in biological materials and was validated by analysing the CRM TORT-1 Lobster Hepatopancreas. Good agreement with the certified (330+60 yg 1-l) value was achieved (353k64 yg 1-l). The analysis of coastal water samples from Sutton Harbour, Plymouth, showed that mercury levels ranged from 24 4 5 to 54+10 ng 1-'.
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