Relationship Between Freshwater Harmful Algal Blooms and Neurogenerative Disease Incidence Rates in South Korea

Background: Due to anthropogenic activities and global warming, the severity and distribution of harmful algal blooms (HABs) have been increasing steadily worldwide, including in South Korea (S. Korea). Previous studies reported exposure to HABs can increase the risk of HAB-related diseases. However, very few studies examined the linkage between HABs and disease occurrence, particularly in S. Korea. The objective of this study was to evaluate the potential impact of HABs on neurodegenerative diseases (NDs), including Alzheimer’s disease, Parkinson’s disease, and motor neuron disease, at a population level. Methods: : Thirteen year data (2005-2017) for chlorophyll- a (chl-a) concentrations as a bloom-related parameter, annual numbers of NDs and population information were collected. First, the entire area of S. Korea was divided into a grid of 1-km and the population number in each 1-km grid was collected using Statistical Geographic Information Service Plus system. Cross-sectional time series data were analyzed with two statistical models, a generalized linear mixed model and a generalized linear model. Results: : The results show that there is a general trend of increasing chl-a concentration and NDs year by year. We observed positive correlations between HAB intensity and incidence rate of NDs. Particularly, HABs seem to have the most long-term carry-over effect on Parkinson’s disease. Another key finding was that a 5-km radius from the HAB location was the boundary that showed most significant associations with three NDs. Conclusions: : This study provides statistical evidence that supports the potential risk of NDs from the exposures of HAB. Thus, it is recommended to monitor a broad spectrum of cyanotoxins, including neurotoxins, in the areas of bloom-affected regions in S. Korea as well as epidemiological studies in the future.