San Joaquin Valley 
Stormwater Quality Partnership



Mercury Hazards

Mercury Harms Humans
Elemental mercury and all of its compounds are toxic, exposure to excessive levels can permanently damage or fatally injure the brain and kidneys.

Elemental mercury can also be absorbed through the skin and cause allergic reactions. Ingestion of inorganic mercury compounds can cause severe renal and gastrointestinal damage. Organic compounds of mercury such as methyl mercury are considered the most toxic forms of the element.

Exposures to very small amounts of these compounds can result in devastating neurological damage and death.

For fetuses, infants and children, the primary health effects of mercury are on neurological development. Even low levels of mercury exposure such as result from mother's consumption methylmercury in dietary sources can adversely affect the brain and nervous system. Impacts on memory, attention, language and other skills have been found in children exposed to moderate levels in the womb.

The cycle of mercury in nature is complex.
This illustration summarizes how methylmercury accumulates at the higher levels of the food chain and becomes concentrated in fish and animals that eat fish.

(1) Source 1
Methylmercury in the water and sediment is taken up by tiny animals and plants known as plankton.

(2) Source 2
Minnows and juvenile fish eat large quantities of plankton over time.

(3) Source 3
Larger predatory fish consume many smaller fish, accumulating methylmercury in their tissues. The older and larger the fish, the greater the potential for high mercury levels in their bodies.

(4) Source 4
Fish are caught and eaten by humans and animals, causing methylmercury to accumulate in human tissues.

(Source: National Institute of Health,

mercury poisoning
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Delta Methylmercury Control Program

The Delta Methylmercury Control (DMC) Program applies specifically to the Delta and Yolo Bypass waterways.

The DMC program is designed to protect people eating one meal/week (32 g/day) of trophic levels 3 and 4 Delta fish, plus some non-Delta (commercial market) fish.

Some consumers eat four to five meals per week (128-160 g/day) of a variety of Delta fish species. The fish tissue objectives will be re-evaluated during the Phase 1 Delta Mercury Control Program Review and later program reviews to determine whether objectives protective of a higher consumption rate can be attained as methylmercury reduction actions are developed and implemented.

Additional information about methylmercury source control methods must be developed to determine how and if Dischargers can attain load and waste load allocations set by the State. Information is also needed about the methylmercury control methods' potential benefits and adverse impacts to humans, wildlife, and the environment.

Therefore, the DMC Program will be implemented through a phased, adaptive management approach.

More information about Delta Methylmercury Control Program:



Posted by Koosun Kim

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