The Guadalupe watershed was an area of high activity during the
California Gold Rush, and as a result,
Mercury toxicity and its effects on surrounding citizens and wildlife is a major concern for the area, and monitored intensively. Because
mercury is an effective magnet for gold, miners during the Gold Rush would regularly line their sluices with mercury to amalgamate the gold out. An estimated 6,500 tons of mercury was lost in the system of creeks and rivers along the coast between 1850 and 1920, and is still being detected today in the water, animal life, and riverbeds of these affected tributaries. The effects of mercury on aquatic environments are very complex and create a number of health and safety risks. The most dangerous effect is its conversion into
methylmercury by bacteria in rivers and lakes, which is in fact a more toxic substance than plain mercury. Methylmercury has a capacity to be taken in by insects and other
invertebrates which the fish eat, which are in turn consumed by humans. Through this process of
biomagnification, the methylmercury concentration increases the further up the food chain it reaches.
Health effects Methylmercury is known for impairing neurological development in fetuses, infants, and small children. Exposure in the womb from a mother's consumption of contaminated fish and shellfish can harm a baby's newly developing brain and nervous system. There are notable impacts on cognitive thinking, memory, attention, language, and fine motor and visual spatial skills in children that have been exposed to methylmercury in the womb. Methylmercury also causes a number of problems in adults, including impairment of the peripheral vision,"pins and needles" feelings, usually in the hands, feet, and around the mouth, lack of coordination of movements, impairment of speech, hearing, walking, and muscle weakness.
Environmental effects Methylmercury that bioaccumulates in fish and the fish and other animals that eat them can reach harmful levels very quickly. Just how high these levels are depends on several factors, such as local non-air releases of mercury, naturally occurring mercury in soils, physical and biological properties of the water-body in question, and the age, size, and types of food the fish eats. Birds and mammals that eat fish are the most affected in the ecosystem because of their placement as predators in the food chain. Effects of methylmercury exposure on wildlife include death, as well as reduced fertility, slower growth and development, and abnormal behaviors that can drastically effect the animals survival. == Santa Clara Valley Water District involvement ==