Undergraduate Research and Creativity

URECA

2008-2009

An assessment of quaternary ammonium compounds in biosolids

Daryl McHugh, Joseph Ruggieri, Xiaolin Li, and Bruce Brownawell
School of Marine and Atmospheric Sciences

Biosolids are the solid portion of treated sewage sludge that may be recycled as compost for the beneficial use of their nutrient-rich organic materials. By far, the largest sector of beneficial reuse of biosolids is land application in agriculture. Other beneficial areas include commercial and domestic landscaping/gardening, forestry and mine reclamation. Alternative fates of biosolids are storage, landfilling and incineration, with incineration being most common. Biosolid composting is appealing because it appears to provide a beneficial recycling of sewage sludge, which had previously been incinerated, landfilled or dumped into open waters to a large extent. Such practices are seen as environmental risks. The past several years have witnessed an increase in biosolids production and reuse, both in the U.S. and abroad (especially Europe). A 1999 EPA report estimated that 6.9 million dry tons of biosolids were generated in 1998 in the U.S., with approximately 60% beneficially reused. By 2010, it is projected that 8.2 million dry tons of biosolids will be produced, with 70% beneficially reused. Now, there is increasing concern as to potential environmental and health risks associated with the application of biosolids in agriculture. There is much uncertainty about the presence and concentration of contaminants in biosolids, especially organic chemicals used in pharmaceuticals and personal care products.

This research is the first study to examine the fate and concentration of the class of organic contaminants known as quaternary ammonium compounds (QACs). QACs are an important class of cationic surfactants used in fabric softeners, personal care products and antimicrobials. QACs strongly sorb to solid matrices, providing a possible reason why they are persistent in biosolids. An initial assessment of the distribution of 19 QACs in samples indicates total QAC concentrations varying between 190 and 760 μg/g. Approximately half of the total QAC concentrations may be attributed to C16:16, C16:18 and C18:18 dialkyldimethylammonium compounds, which are used in fabric softeners. A critical discovery is the exceptionally high levels of C22 alkyltrimethylammonium, a previously unreported persistent environmental contaminant. Biosolid samples collected in 2003 had C22 alkyltrimethylammonium concentrations varying between 22 and 53 μg/g, while 2009 samples had concentrations as high as 290 μg/g. This compound is an ingredient in many hair care products, whose use has increased exponentially in recent decades. The high levels of QACs (especially the previously unmeasured C22 alkyltrimethylammonium) makes the study of biosolids of the utmost importance. In addition to these QAC compounds, the levels of QACs will be compared to those previously recorded contaminants found in biosolids and offer an evaluation of present regulatory laws and policies concerning the use of biosolids.

We are grateful for the support of the NIEHS Superfund Basic Research Program that sponsored this study under grant ES07384.