The issue of mercury, specifically the variant methylmercury, is a public health concern because sport fishing is practiced all year in and around the Delta watershed.
The high mercury rates are a legacy from the state's mining operations in the late 19th and early 20th centuries, when mercury ore was mined from 240 mines statewide and used to amalgamate gold and silver.
The mercury that eventually ran into streams and rivers was inorganic and not easily absorbed into the tissues of fish. However, once that mercury moves downstream, bacteria convert it into methylmercury, which can be absorbed.
As it moves up the food chain, it is found in highest concentration in the tissues of large and long-lived predatory fish at the top of the food chain – such as striped bass.
Methylmercury affects the brain and nervous system. In low doses, it can affect child developmentby delaying walking and talking, and can result in a shortening of attention span as well as in learning disabilities. In adults it can affect fertility and blood pressure regulation and can cause vision and memory loss.
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