Chronic exposure to domoic acid

3 February 2020 – News

As oceans continue to warm, harmful algal blooms (HABs) are becoming more frequent, more toxic and longer lasting. This is affecting the safety of our seafood as domoic acid (a neurotoxin produced by some diatoms) produced by these events accumulates in feeding fish and shellfish.

High levels of domoic acid (DA) can lead to gross histopathological lesions in the hippocampus and permanent memory loss in both marine mammals and humans. DA was first recognized as a seafood toxin in 1987 when more than a hundred people became ill after consuming contaminated mussels. As a result, the seafood safety regulatory limit was set at 20 mg DA/kg shellfish. There is, however, still no limit for long-term, low-level but repeated exposure to DA.

This investigation aimed to determine if chronic exposure to low doses of DA impairs cognitive function. Cohorts of female mice were created to evaluate spatial learning, memory and activity level. Hippocampal damage was also examined through brain immunohistochemistry and histology assessments. Studies were made at 25 and 36 weeks and included the control groups.

The findings suggest that exposure to low asymptomatic doses of DA can lead to cognitive deficits and hyperactivity – signals that seem to be reversible after six months recovery (no toxin exposure). No gross morphological lesions in hippocampal region were identified.

These results contrast with cases of acute exposure, in which, in addition to activity level changes, impairment of spatial memory and learning impairment, brain lesions occurred frequently.

As a mammalian model was used, we can expect similar results in humans and sea mammals so it is important that those responsible for marine wildlife health, as well as seafood companies, take into account the potential negative effects of persistent low-level exposure to DA.

Lefebvre K. et al. Chronic low-level exposure to the common seafood toxin domoic acid causes cognitive deficits in mice. Harmful Algae 64 (2017) 20–29. http://dx.doi.org/10.1016/j.hal.2017.03.003