Evaluating microcystin exposure risk through fish consumption

Abstract

Microcystin is a cyanobacterial hepatotoxin that is found worldwide, and poses a serious threat to the ecological communities in which it is found as well as to those who rely on these waters for drinking, sanitation, or as a food source. Microcystin is known to accumulate in fish and other aquatic biota, however the prevalence of microcystin in fish tissue and the human health risks posed by microcystin exposure through fish consumption remain poorly resolved. Here we show that microcystin is pervasive in water and fish from several tropical (Ugandan) and temperate (North American) lakes, including lakes that support some of the largest freshwater fisheries in the world. We establish that fish consumption can be an important and sometimes dominant route of microcystin exposure for humans, and can cause consumers to exceed recommended total daily intake guidelines for microcystin. These results highlight the importance of monitoring microcystin concentrations in fish, and the need to consider potential exposure to microcystin through fish consumption in order to adequately assess human exposure risk.

Figure 1

Regression of microcystin concentrations against total phosphorus concentrations from all study sites (r²_adj: 0.40, n=72, P<0.001). Site labels in Figure 1 are indicated as follows: A (Lake Albert), En (Lake Edward nearshore), Eo (Lake Edward offshore), G (Lake George), Mb (Lake Mburo), M (Murchison Bay, Lake Victoria), N (Napoleon Gulf, Lake Victoria), Nk (Lake Nkuruba), S (Lake Saka), MB (Maumee Bay, Lake Erie), Q (Bay of Quinte, Lake Ontario).

Figure 2

Microcystin concentrations in several species of fish. The red line represents the fish microcystin concentration that would cause a consumer to exceed tolerable daily intake (TDI) values recommended by the WHO for chronic exposure (0.04 μg/kg body weight/day; which yields a threshold concentration of microcystin in fish of 24 μg/kg wet weight for an individual weighing 60 kg and consuming 100 g of fish/day).

Figure 3

Potential daily microcystin exposure for individuals consuming water and fish from the study lakes. The reference line indicates the threshold value at which a 60 kg consumer would exceed the WHO TDI (2.4 μg/day). Exposure from water is indicated in black, and is based on daily consumption of 2 L using mean microcystin concentrations in water. Exposure from fish is indicated in grey, and is based on daily consumption of 100 g using mean microcystin concentration in the fish taxa with the highest mean concentrations. The species used in calculating exposure from fish are indicated as follows: Ln (Lates niloticus), Ol (Oreochromis leucostictus), Oe (Oreochromis esculentus) Ra (Rastrineobola argentea), Pr (Poecelia reticulata), H (Haplochromis spp.), A (alewife), and W (walleye).