Neurological Diseases and Disorders
Impacts on Risk
Numerous recent reports have described observed and anticipated detrimental effects of climate change on ocean health, resulting in increased risks to neurological health from ingestion of or exposure to neurotoxins in seafood and fresh and marine waters. Neurotoxins produced by harmful algal blooms and other marine microorganisms can cause serious illness and death in humans. Under the correct conditions, harmful algal blooms produce potent neurotoxins that are often taken up and bioaccumulated in filter-feeding molluscan shellfish including oysters, clams, and mussels, as well as by certain marine and freshwater fish. The most frequent human exposures are via consumption of seafood containing algal toxins, although some toxins may be present in freshwater sources of drinking water, and others may be aerosolized by surf breaking on beaches and then transported by winds to where they can cause respiratory distress in susceptible individuals who breathe them. Because cooking or other means of food preparation do not kill seafood biotoxins, it is essential to identify contaminated seafood before it reaches consumers. Health effects including amnesia, diarrhea, numbness, liver damage, skin and eye irritation, respiratory paralysis, and PD- and AD-like symptoms may be severe, chronic, and even lead to death. It has recently been reported that even a single low-level exposure to algal toxins can result in physiological changes indicative of neurodegeneration. Work done on biotoxin-related neurologic disease in marine mammals indicates that domoic acid exposure can cause acute neurologic symptoms by crossing the placenta and accumulating in the amniotic fluid where it can impact neural development in the fetus, alter postnatal development, and lead to chronic illnesses such as epilepsy. Climate change may alter the geographic range in which harmful algal bloom toxins appear, the frequency of toxin production, and the actual delivery of toxins (both increasing and decreasing in some cases) due to extreme weather. Harmful algal blooms are increasing in frequency, intensity, and duration globally, partially as a result of climate change, although this link is poorly understood. Nonetheless, it is clear that changes in precipitation and ocean temperatures, coupled with increased nutrient loading, may lead to earlier seasonal occurrence, as well as longer lasting and possibly more toxic harmful algal blooms. Emerging research suggests that exposure to a number of agents whose environmental presence may increase with climate change may have effects on neurological development and functioning. For example, exposure to pesticides and herbicides during specific developmental windows, in combination with other exposures later in life, could increase the risk of PD and other neurological diseases. Exposure to heavy metals is known to exacerbate neurological deficits and learning disabilities in children, and is suspected of being associated with both onset and exacerbation of AD and PD. Evidence suggests that early-life occurrence of inflammation in the brain, as a consequence of either brain injury or exposure to infectious agents, also may play a role in the pathogenesis of PD. In addition to conditions such as PD and AD, post-traumatic stress disorder (PTSD) is likely to have profound effects on the neurological functioning of populations exposed to the stress of extreme weather events, and the resulting dislocation and deprivation that may result from climate change.