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Event name:
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US-20-005
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Country:
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UNITED STATES
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Nature of the harmful event:
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Water Discoloration
,
Seafood toxins
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Event directly affected:
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Other Terrestrial
,
Shellfish
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Toxicity detected:
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Yes
(Approximate range: 1.5-5.7 ppb microcystin-RR in oysters)
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Associated syndrome:
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OTHER
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Unexplained toxicity:
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No
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Species implicated in toxin transmission (transvector):
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Report the outcome of a monitoring programme:
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Yes
(Connecticut Department of Agriculture Bureau of Aquaculture (DABA))
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Event occurred before in this location:
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No
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Individuals to contact:
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VAN GULICK, Emily
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Causative organism known:
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Yes
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Causative Species/Genus:
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Microcystis aeruginosa
( cells/L)
<5-10% phytoplankton composition of samples from Greenwich Cove. Microcystis was not present in Binney Pond on 7/17. Dr. Dianne Greenfield, a DABA colleague, confirmed the presence of Microcystis aeruginosa in subsequent samples she collected.
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Co-Ocurring Species/Genus:
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Chlorophyll concentration, if known:
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µg/l
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Additional bloom information:
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No cyanobacteria blooms were observed by DABA staff in freshwater or estuarine environments. Phytoplankton samples revealed the presence of "stressed" Microcystis colonies in Greenwich Cove (<5-10% composition of samples). Greenwich Cove was precautionarily closed on 7/16. Oyster samples taken from Greenwich Cove (commercial lots: Mayhew North and Mayhew South) both had low concentrations of microcystin-RR (3.2 and 3.0 ppb, respectively). Microcystin-RR was present in the Mayhew South lot oysters for multiple months (maximum concentration 5.7 ppb on 9/29); however, it was never detected in the adjacent Mayhew North lot again. Testing of Mayhew South was sporadic due to the expense of UPLC-MS/MS testing (~$250/sample), slower turn-around-time than in-house testing performed by the DABA lab, and the knowledge that shellfish can take an extended period of time to depurate cyanotoxins (weeks-months). Given staff limitations, the area was not surveyed again for blooms (and no blooms were reported again), but oyster testing continued until MC-RR was no longer detected. The maximum MC-RR concentration from Mayhew South was detected on 9/29; therefore, subsequent blooms could have occurred and were not reported to DABA, or MC-RR concentrations in oysters increased naturally during the depuration process (which has been noted in multiple shellfish cyanotoxin depuration studies).
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Event-related bibliography:
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Species containing the toxin
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Toxin type
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Toxin details
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Max. concentration
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Assay type
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Eastern oyster
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Microcystins
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5.7 ppb (ng/g)
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LC
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Kit used:
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Type of kit used:
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Additional information:
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UPLC-MS/MS performed by UCONN Center for Environmental Sciences and Engineering (CESE). Limit of detections reported as: cylindrospermopsin (3.0ppb), anatoxin A (1.7ppb), microcystin-RR (1.5ppb), microcystin-YR (15ppb), microcystin-LR (15ppb), microcystin-LA (7.5ppb). Note that the LOD for microcystin-RR is much lower than the other microcystins, and there are 250+ variants; therefore, it is possible that other MCs were present in oysters, but only MC-RR was detected due to low concentrations and testing limitations.
The DABA also screened 2 oyster samples in July for saxitoxins using PSP scotia rapid test kits (FDA approved limited use method), which were negative.
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Economic losses:
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The total commercial economic loss due to closures was estimated at ~$125,000, which compounded additional losses due to COVID-19.
There is a recreational (conditionally approved seasonal) area in Greenwich Cove. The reopening was delayed ~1 month.
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Management decision:
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Since cyanotoxins are not yet regulated by the FDA in shellfish, the DABA left the area precautionarily closed until MC-RR was no longer detectable. Mayhew North was reopened in August, while Mayhew South remained closed until December.
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Additional harmful effect information:
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While this was not reported, Binney Pond is surrounded by a park and DABA staff observed many children, families, and dogs at the park on 7/17 during bloom investigation. It is possible that there is a human health impact from exposure to bloom water.
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