William Gross, in his Aug. 13 column, “Maine Voices: EPA distorts basic science of organic chemistry by calling CO2 ‘pollution,’ “ presents a nonsensical argument against treating carbon dioxide as a pollutant.

Classification of pollutants is not black and white as Mr. Gross suggests. Many elements and natural compounds essential to life can become pollutants when present in the environment at excessive concentrations.

For example, selenium is a micronutrient essential to maintaining human health, but long-term consumption at excessive levels can lead to health problems. Mr. Gross states that tomato plants grow well in an atmosphere enriched in carbon dioxide.

As someone with a background in geochemistry (and experience in growing tomatoes), I know nitrogen and phosphorus are essential nutrients for tomato plants (and all other plant life), and when available in soil at proper concentrations, these nutrients lead to optimum tomato production.

When these nutrients are present in lakes and streams at excessive concentrations, however – commonly the result of urban runoff, wastewater discharge and agricultural use – they can cause algal blooms, eutrophication (reduced oxygen) and other water-quality problems, as the residents of Toledo, Ohio, were recently made aware. Just because higher concentrations of carbon dioxide boost tomato production in a greenhouse does not mean carbon dioxide cannot be treated as a pollutant. The world is not that simple.

Unfortunately, many arguments against stricter environmental regulation published in this paper and elsewhere are based on an incomplete or incorrect understanding of the science they cite.

Robert J. Rogers, Ph.D.