Amid unusually heated rhetoric, the U.S. Senate on June 20 defeated efforts to nullify the Mercury and Air Toxics Standards, known as MATS. Proposed by the Environmental Protection Agency, MATS establishes national limits for mercury and other toxic substances released into the air by power plants. Limits would become effective in 2016. The resolution to nullify MATS was defeated 53 to 46. Five Democrats voted for nullification. Five Republicans, including Tennessee's Lamar Alexander, voted to uphold the measure.

From a medical standpoint, the debate boils down to jobs versus the health of children. An overlooked question: How many jobs are worth the health of one child?

Mercury is an unforgiving, environmental toxin. One-third of the mercury in our environment stems from natural sources -- volcanic eruptions and natural erosion of rocky formations. One-third arises from coal-fired power plants. Other important sources include cement kilns, factories that manufacture bleach and pool chemicals, gold mining and trash incinerators.

Once mercury is dispersed into the atmosphere, it may circulate for years before eventually settling in fresh and salt waters. Elemental mercury is toxic whether inhaled or ingested, exposing brain and kidneys to injury. Much more toxic is methyl-mercury (MeM). Micro-organisms in the waters slowly convert insoluble, elemental mercury to MeM, which is rapidly absorbed by all organisms. Through a process of "bio-magnification" MeM is progressively concentrated as smaller life forms are eaten by larger and larger fish and aquatic mammals.

Concentration of MeM in freshwater fish has led to health advisories for consumption of catches in many locales, including some streams in Tennessee. Certain species of seafood, including swordfish, ahi tuna and mackerel concentrate MeM, which poses health risks to fetuses and young children. No method of preparation or cooking can remove MeM from fish.

In a pregnant woman, MeM rapidly crosses the placenta to enter the fetal circulation. MeM easily crosses the blood-brain barrier to enter the developing nervous system. Clear correlations exist between MeM levels and neurological development, including later behavioral and intellectual outcomes. These findings account for advisories for fish consumption for expectant mothers.

MeM toxicity has been verified in a variety of laboratory settings in which tissue cultures, rodents and monkeys were exposed to levels encountered in human environments. Ongoing studies of island children whose mothers were exposed to high MeM levels from fish consumption during pregnancy validate the lab findings. Children who live downstream from gold-mining sites in the Amazon River basin show similar correlations between MeM exposure and brain and motor abnormalities.

Brain abnormalities range from slowed performance on intelligence tests to seizures. Children may exhibit emotional outbursts. Motor performance problems range from clumsiness to complete lack of coordination. The devastation caused by MeM is permanent.

States cannot properly handle environmental standards for air and water since neither respects political boundaries. Highly toxic materials, such as mercury and its related soluble compounds need enforceable international standards. Consider the rapid proliferation of coal-fired power plants in China as an example of threats to the health of our children.

Lobbyists representing the coal and power-producing industry, cement manufacturers and some chemical industries argue that MATS and similar environmental regulation destroy jobs and raise the costs of producing electricity and a host of goods. The closeness of the recent vote to sustain MATS reflects the power of this argument.

But new technologies to limit MeM and other toxic pollutants lead to the creation of new types of jobs. Many coal-fired power plants have already installed effective anti-pollution devices. Every power plant must acknowledge its moral responsibility to the health of children. Consider this the moral overhead of doing business.

Our senators and other national and state legislators would benefit by paying closer attention to environmental science and less to lobbyists.

Wendell Berry's masterful poem, "Questionnaire," expresses the issue of jobs versus health in unforgettable terms. Access the poem at www.everydayliturgy.com/questionnaire-by-wendell-berry.

Email Clif Cleaveland at cleaveland1000@comcast.net.