August 2010, Vol. 22, No.8

Research Notes

Potential Benefit for Biosolids Land Application in Tropics

Biosolids land application can help improve agricultural production and maintain soil fertility, especially in the tropics, researchers have found. In an effort to determine how land application affects the amount of organic matter in soil, researchers from the Brazilian agricultural research corporation Embrapa (Brasilia) evaluated the changes in total soil organic carbon after extensive land application.

The researchers looked at the chemical characteristics of the organic matter’s main constituents, known as “humic substances,” according to a news release from the Soil Science Society of America (Madison, Wis.).

Biosolids contain organic matter and nutrients, such as nitrogen and phosphorus, that can improve soils, the study says. This potential could be important in tropical regions, where a higher level of microbial activity from high temperatures and humidity accelerates the decomposition of organic matter, leading to sandy soils. In Brazil, the potential benefit may be even more important, because most soils there have high clay-to-mineral ratios and are especially poor in organic matter, the news release says.

For the 7-year study, conducted by professor Wanderley Melo of the State University of Sao Paulo–UNESP, researchers used chemical and spectroscopic analyses to evaluate the effect of biosolids on organic matter in clay and sandy soils from tropical areas of Brazil, the news release says. Results, published in the January/February issue of the Soil Science Society of America Journal, showed an increase in organic content in both types of soils, with a higher relative increase in sandy soils.

Spectroscopic analysis detected chemical changes in the organic matter and its humic acids that resulted in biosolids being incorporated into the soil as humic substances instead of remaining as less transformed organic material that easily converts to carbon dioxide and augments greenhouse gas emissions. The resulting humic substance is a more resistant class of soil chemical compound with a longer lifetime in soils than fresh or only slightly transformed organic material, the news release says.

The study’s results could offer a solution that enables tropical soils to maintain or increase the levels of organic matter, according to the news release. More field and laboratory experiments are needed to better understand the dynamics of soil organic matter and the potential for carbon management in soils, including soil carbon sequestration.

Funding for the study was provided by the Sao Paulo Research Foundation, the Brazilian National Council for Scientific and Technological Development, and the Optics and Photonics Research Center. 

Household Cleaning Products Pose a Potential Threat to Health

Certain chemicals in household cleaning products could lead to the formation of probable human carcinogens. An article published in the American Chemical Society (ACS; Washington, D.C.) journal Environmental Science & Technology says scientists have found evidence that some ingredients in shampoos, detergents, and other cleaning agents may be a source of precursor materials for the formation of the water supply contaminant N-nitrosodimethylamine (NDMA).

NDMA is a nitrosamine that has been found to form during the disinfection of drinking water, wastewater, and recreational water. The U.S. Environmental Protection Agency has classified several nitrosamines, including NDMA, as probable human carcinogens, an ACS news release says.

Past studies have found that waters receiving discharges from wastewater treatment plants are prone to forming NDMA when chloramines are added. Chloramines are a class of water disinfectant formed by a combination of chlorine and ammonia. However, the identity of the responsible precursors was unclear. Past studies found that quaternary amines, which are ingredients in cosmetics, contained nitrosamines.

Because NDMA precursors were associated with wastewater discharges, William A. Mitch of the Department of Chemical Engineering at Yale University (New Haven, Conn.) and his colleagues hypothesized that their source was consumer products.

To test the theory, the researchers tested four consumer products and an array of quaternary amines for their potential to form nitrosamines. The results showed that, when mixed with chloramines, quaternary amines and some household cleaning products formed NDMA, but the mixtures varied in their ability to transform, the news release says.

While the study supported the role of quaternary amines in the formation of nitrosamines, it was not able to quantify the contribution of consumer-product-based quaternary amines to NDMA formation during disinfection. Current analytical techniques are not able to measure polymeric quaternary amine concentrations in wastewater effluents, so their importance for NDMA formation remains unclear, Mitch explained.

The researchers note that wastewater treatment plants may remove some quaternary amines, but because they are major ingredients in a variety of consumer products, a significant amount may persist. The combination of disinfectants and quaternary amines also could occur in other places, such as swimming pools or mixtures of different household cleaners, the news release says.


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