- About SRWP
- Explore the Watershed
- A Roadmap to Watershed Management
- Sacramento River Basin Report Card
- Cover and Acknowledgements
- Table of Contents
- List of Acronyms
- Executive Summary and Report Card
- 1.0 Introduction and Background
- 2.0 Indicator Selection
- 3.0 Indicator Generation, Evaluation, Aggregation
- 4.0 General Methods and Principles
- 5.0 Interpretation
- 6.0 Conclusions and Recommendations
- Appendix A: Glossary of Terms
- Appendix B: Indicator Selection Criteria
- SWIM Digital Atlas
- SWIM Digital Library
- Invasive Plants
- On-Line Regulatory Permitting Guide
- Rural Residential Development
- Our Work
- Conferences and Workshops
- Monitoring Committee
- River of Words
- Journey through the Sacramento River Watershed
- Sacramento River Watershed Partners
Mercury Pollution Considerations
The Industrial Revolution, which generated widespread contamination of terrestrial and aquatic environments by mercury and its compounds, has greatly enhanced the level of atmospheric mercury.
The mining of mercury and its subsequent release into the atmosphere, the burning of fossil fuels, cremation off-gasses and disposal of batteries, fluorescent bulbs and other mercury-containing products into landfills have provided a continuing release of mercury which has been transported into the atmosphere and over the entire surface of the earth.
As it circulates in the atmosphere the mercury is oxidized and settles back to earth in rainfall. When mixed with soil and sediment some of it is transformed to elemental mercury and recycles back into the atmosphere. In addition plants appear to act as a buffer, absorbing mercury when atmospheric levels are high and releasing it when atmospheric levels are lower.
Mercury and its compounds readily attach to particulate material in soil and sediment. In the presence of living organisms (especially sulfate-reducing bacteria) ionic mercury can transform into monomethylmercury and dimethylmercury. When exposed to sunlight the (di)methylmercury is photodegraded to monomethylmercury, usually near the surface of water, and methane gas is released. Methylmercury is stable and readily penetrates through cell membranes and complexes with essential cellular components.. In humans, methylmercury can be absorbed through the skin or intestinal tract as well as the lungs. It is a cumulative poison which can be highly toxic and/or lethal.
Mercury and its compounds are cumulative toxins with no known beneficial physiological function in bacteria, plants or animals. The degree of toxicity depends upon the solubility and the capacity for absorption into the organism.
Once inside the body mercury and its compounds become widely dispersed in blood and tissues and have the capacity to cross the blood-brain barrier and accumulate in the brain and nervous system. It can cross the placenta into the fetus and since it can also become a component of mothers' milk it poses a particular hazard to the fetus and nursing offspring.
The fetus and infant are much more sensitive (5 - 10x) to mercury toxicity than adults but the symptoms are often delayed or hidden for long periods after exposure.
In fish, mercury accumulates predominantly in the liver and muscle tissues, primarily in the monomethyl form, which is why it posses a potential human toxicity problem following consumption of fish fillets.
In humans the most commonly recognized site of mercury damage is the brain. The effects are generally irreversible, resulting in local cell death and, in extreme cases, blindness, coma and death. However less than 10% of the total body burden of mercury is found in the brain and the remainder is distributed in all cells of the body.
Methylmercury is an extremely effective agent for chromosome breakage and inactivation of the mitotic spindle. It appears to attach to sulfhydryl groups on enzymes and it inactivates the microfilaments involved in cell migration. It is a thousand times more potent than cochicine, the agent usually used in the laboratory to halt mitosis. It can also combine and inactivate DNA and RNA in cells.
Additional investigation based on cell processes such as mitosis, cell movement and capacity to engulf foreign material is urgently needed to supplement current tests based on mercury's effects on the nervous system.
Elemental Focus on Mercury (Spring 2001)
BEC Environmental News
Chemical Fact Sheet: Mercury (1997-98)
Handbook of Chemistry and Physics