Cyanotoxins in Tidal Waters of Chesapeake Bay

Cyanobacteria blooms have long been described for Chesapeake Bay nontidal and tidal waters, but measurable toxin has only been recently recorded. During September 2000, the earliest tidal-water records of cyanotoxins in the Bay identified microcystin from a Microcystis-dominated bloom on the Sassafras River. Between 2000 and 2006, opportunistic samples collected from cyanobacteria blooms were analyzed for toxin concentration to better inform natural resource, agriculture, and human-health management agencies on potential bloom-related health risks. The hepatotoxin microcystin was detected most frequently and over a range of concentrations from 2.9 × 10−2 to 6.58 × 102 μg L−1. Microcystin levels exceeded literature-based chronic drinking-water guidance values of 1 μg L−1 and recreational safety guidance for children of 10 μg L−1 in 71% and 31% of samples, respectively. Samples from tidal fresh and oligohaline habitats showed a log-normal distribution of toxin concentrations, and microcystin had positive log-linear relationship with Microcystis aeruginosa cell counts (r2 = 0.42). A subset of the samples positive for microcystin was also tested for neurotoxins and showed anatoxin-a as the next-most common toxin encountered (46% of samples tested) at concentrations from 3 × 10−3 to 3 μg L−1. Saxitoxin (PSP-toxin) was present in trace amounts (3 × 10−3 μg L−1) in one sample. Cylindrospermopsis raciborskii has occasionally been found in abundance, but all tests for cylindrospermopsin were negative. Microcystin and anatoxin-a have been identified in association with fish kills, bird kills, and human-health events. Virginia and Maryland state management agencies conducted beach closures during 2000, 2003, and 2004 and provided waterway health advisories in 2005 and 2006 in response to the findings.