Lethal Effects of Mercurials

Data sets for mercury are now available for locations in the Adriatic Sea, Alaska, Antarctica, Brazil, Canada, China, Cuba, Florida, Greenland, India, Italy, Korea, Malaysia, New Jersey, Puerto Rico, Spain, Taiwan, Tennessee, Thailand, and Viemam. 

Death is the only biological variable now measured that is considered irreversible by all investigators. Nevertheless, time of death is modified by a host of physical, chemical, biological, metabolic, and behavioral variables and it is unfortunate that some regulatory 

The marine ciliate protozoan Uronema marinum, with an LC50 (24 h) value of 6.0(jtg/L, failed to develop resistance to mercury over an 18-week period. However, another marine ciliate protozoan, Uronema 

0 (xg Hg/L, as HgCh. Death was preceded by polyp contraction during the first 8 h, color loss within 24 h, and tissue loss within 48 h. 

Many acute toxicity bioassays were of 96 h duration, a duration that allows the senior investigator and technicians alike the opportunity to enjoy an unintermpted weekend. But it is clear that assays of 168-h duration produced LC50 values up to 45 times lower (more toxic) than did the 96-h assays, as was shown for mud snails. It is recommended that acute toxicity bioassays with mercury and other toxicants and estuarine fauna should consist of a minimal 10-day continuous exposure followed by a 10-day observation period. 

---

A review of the lethal and sub-lethal effects of mercury on aquatic life... 

Boney, a. D. Sub-lethal effects of mercury on marine algae. Marine Pol. Bull. 2, 69 (1971). 

Evidence suggests that lead exacerbates the toxic effects of mercury. In the rat, the administration of lead nitrate increased kidney and liver glutathione content and resulted in increased mercury deposition in the kidney, along with increased lethality in rats (Congiu et al. 1979). 

Thain, J.E. 1984. Effects of mercury on the prosobranch mollusc Crepidula fornicata acute lethal toxicity and effects on growth and reproduction of chronic exposure. Mar. Environ. Res. 12 285-309. 

In animal models, dimercaprol prevents and reverses arsenic-induced inhibition of sulfhydryl-containing enzymes and, if given soon after exposure, may protect against the lethal effects of inorganic and organic arsenicals. Human data indicate that it can increase the rate of excretion of arsenic and lead and may offer therapeutic benefit in the treatment of acute intoxication by arsenic, lead, and mercury. 

The lethal effects of methylmercury in various species of mammals are influenced by ambient temperature, dietary selenium, ethanol, and especially hypertension. Tests with a genetic strain of rat with high blood pressure showed that this strain was more sensitive to methylmercury than were control strains they died earlier and with higher tissue mercury burdens. Because hypertension and borderline hypertension is common among human inhabitants of mercury-polluted areas, with estimates as high as 56% among individuals 40 years old and older, more research seems warranted on the role of hypertension as a significant... 

It is well known that the chemical form of a metal can have a marked impact on its toxicity, e.g., Stephenson and Taylor (1975) foimd that the lethal effect of copper on Venerupis decussata could be reduced substantially by adding EDTA to the test solutions and thereby converting toxic ionic copper into a less toxic organic complex. Mercury entering the aquatic environment may remain in solution eidier dissociated or as a complex, it may become adsorbed by particulate matter or chemically reduced and lost to the atmosphere by volatilisation, or it may be deposited in sediments where many physical, chemical, or biological transformations may occur. 

---