Pyrethroids are now the fourth most used group of insecticides worldwide. Employed in agriculture and in urban areas, they are detected in waterways at concentrations that are lethally and sublethally toxic to aquatic organisms. Highly lipophilic, pyrethroids accumulate in sediments and bioaccumulate in fishes. Additionally, these compounds are demonstrated to act as endocrine disrupting compounds (or EDCs) in mammals and fishes, and therefore interfere with endocrine signaling by blocking, mimicking, or synergizing endogenous hormones through direct receptor interactions, and indirectly via upstream signaling pathways. Pyrethroid metabolites have greater endocrine activity than their parent structures, and this activity is dependent on the enantiomer present, as some pyrethroids are chiral. Many EDCs studied thus far in fish have known estrogenic or antiestrogenic effects, and as such cause the inappropriate or altered expression of genes or proteins (i.e., Vtg-vitellogenin, Chg-choriogenin), often leading to physiological or reproductive effects. Additionally, these compounds can also interfere with other endocrine pathways and immune response. This review highlights studies that focus on the mechanisms of pyrethroid biotransformation and endocrine toxicity to fishes across a broad range of different pyrethroid types, and integrates literature on the in vitro and mammalian responses that inform these mechanisms.

One of the most widely studied organisms responsible for Harmful Algal Blooms (HABs) is the marine dinoflagellate Karenia brevis. This organism produces neurotoxic compounds known as brevetoxins. A related dinoflagellate, Karenia papilionacea, has been reported to occasionally co-bloom with K. brevis but has received little attention as a possible toxin producing species. Therefore, our aim was to investigate the toxin profile for K. papilionacea. A toxic fraction was identified using a cell based cytotoxicity assay and the toxin was isolated and identified as the ladder frame polyether brevetoxin-2 (PbTx-2) using mass spectrometry (MS) and nuclear magnetic resonance (NMR). Toxin production in K. papilionacea increased in response to hypoosmotic stress, as previously observed in K. brevis.