The land application of biosolids for agricultural purposes has long been under the strict scrutiny of environmental regulatory agencies for many components such as metals and pathogens.  More recently, a growing area of public concern – and increased research – has become the presence of microconstituents in biosolids and their persistence in the soil.

Microconstituents, in this context, are primarily considered to be the chemical components of pharmaceutical and personal care products, many of which are of organic origin and which raise the question of potentially negative effects on human and animal health.  New research is focusing on the persistence and bioaccumulation of some microconstituents in land-applied biosolids, and whether or not they present a health risk.  Several studies are assessing an antimicrobial agent called Triclosan (TCS)[1] because it is a common ingredient in many everyday household and personal care products and it is routinely detected in treated biosolids and wastewater treatment plant effluents.

Before looking at the biosolids research, it is helpful to understand the difference between antimicrobials and antibiotics.  These terms are often confused in the public’s mind.  This is understandable since, “all antibiotics are antimicrobials but not all antimicrobials are antibiotics.” (H)  Antibiotics, which at low concentrations inhibit or kill other microorganisms, are molecular substances produced by a microorganism.  They are not synthetic and are often effective on a wide spectrum of microorganisms.  Antimicrobials, on the other hand, include any substance of natural, semisynthetic or synthetic origin that can also kill or inhibit growth of microorganisms.  Some of these have a very narrow window of effectiveness and can be targeted at particular species of microorganisms.  They are considered less likely to cause bacterial resistance over time than repeated antibiotic use.  (H)

The antimicrobial, Triclosan, is a synthetic, broad-spectrum agent that is widely used in consumer products such as antibacterial soaps and body washes, toothpastes, and some cosmetics (A,I) in an effort to reduce or prevent bacterial contamination (FDA).  It can also be found in such disparate items as furniture, clothing, kitchenware, and toys, but the primary use is in antibacterial soaps and washes.  These washes have become consumer favorites since people feel that using them protects them from infection and disease.  Well, the marketing companies have done their jobs well, but their claims are largely unfounded.  Studies have shown that the benefits of using antibacterial soap products are unproven.  In fact, they may contribute to bacterial resistance and have possible hormonal effects. (B)

The Food and Drug Administration (FDA) first reviewed TCS in 2010 and concluded that it was not hazardous to humans (C).  It has since updated its report (B) and is working with other federal agencies to study the effects of TCS on human and animal health as well as its effect on the environment (A,B).  Their investigation only covered antibacterial soaps and body washes that are used with water.  It did not apply to hand sanitizer, hand wipes or antibacterial soaps that are used in health care settings.  The FDA’s conclusion, once again, is that TCS is not known to be hazardous to humans and, in fact, does not provide any extra antibacterial benefit in these products.  The publication stated that there is “currently no evidence that OTC (over the counter) antibacterial soap products are any more effective at preventing illness than washing with plain soap and water.” Ongoing scientific and regulatory review of the safety of TCS stems from the concerns of its possible contribution to making bacteria resistant to antibiotics and the results of animal studies which have shown some alteration in hormonal regulation.

 Research that has already been done on the bioaccumulation and phytoaccumulation of TCS (and TCC) (D, E and F) shows that these antimicrobials are present in biosolids.  Although extensively removed during wastewater treatment, a certain amount of these compounds persist and cling to organic material in the soil after land application.(A)  It is often reported to be one of the most commonly encountered substances in biosolids and wastewater.  (I)  However, in two of the studies that tested vegetables grown in fields amended with biosolids, the detected amounts of TCS and TCC present in the crops were so small as to be considered a negligible exposure to humans.  Consuming these vegetables represented less than 0.5% of acceptable daily intakes (E).  There was also evidence that plants can reduce the leaching of antimicrobials to water resources, thereby reducing the potential impact on human health. (F)  Both of these studies concluded that there is minimal risk to human health from the presence of TCS in crops grown in fields amended with biosolids.

Another study, specifically called “Human health risk assessment of triclosan in land-applied biosolids,” (A) concluded that there are large margins of safety for all pathways of TCS exposure in biosolids and that human health risks from biosolids containing TCS are minimal.  However, the researchers also noted that, due to the ubiquitous presence of TCS in personal care products worldwide, and its inefficient removal during wastewater treatment, this compound should be on the priority list of emerging microconstituent contaminants, and its use in these products regulated. 

While all indicators point to a minimal risk to humans of TCS in land-applied biosolids, ongoing research into this and other microconstituents is warranted to reassure the public of the safety of using biosolids in agriculture.  WERF is beginning just such a study to research priority trace organics, other than TCS and TCC, in biosolids (G).  A more obvious question is the need for such antimicrobials in consumer products at all, especially in light of the research indicating that the compounds like TCS provide no benefit over washing with regular soap and water.  Perhaps a public education campaign to discourage the use of antibacterial products and encourage more thorough hand-washing would help reduce the presence of TCS in biosolids while still protecting human health.  Money talks.  If no one buys these products, the company will stop making them, ultimately reducing the amount of TCS and other antimicrobials in biosolids.  In the meantime, no worries.

1. Versylcke, T; Mayfield, D. B; Tabony, J. A; Capdevielle, M; Slezak, B. “Human health risk assessment of triclosan in land-applied biosolids.” Environmental Toxicology and Chemistry. 14 January 2016.
2. “FDA Taking Closer Look at ‘Antibacterial Soap.”  FDA Consumer Health Information/U.S. Food and Drug Administration. December 2013.
3. “Triclosan: What Consumers Should Know.”  FDA Consumer Health Information/U.S. Food and Drug Administration.  April 2010.
4. Cha, J; Cupples, A.M.  “Detection of the antimicrobials triclocarban and triclosan in agricultural soils following land application of municipal biosolids.”  Water Resources. 2009 May; 43(9):2522-30.
5. Prosser, R.S; Lissemore, L; Topp, E; Sibley, P.K.  “Bioaccumulation of triclosan and triclocarban in plants grown in soils amended with municipal dewatered biosolids.”  Environmental Toxicology Chemistry. 2014 May; 33(5):975-84.
6. Aryal, N; Reinhold, D.M.  “Phytoaccumulation of antimicrobials from biosolids: impacts on environmental fate and relevance to human exposure.”  Water Resources. 2011 November1;45(17)5545-52.
7. “Water Environment Research Foundation Begins Research on Priority Trace Organics in Biosolids.” Press release from WERF. 31 March 2016.
8. “Antimicrobials: An Introduction” Antimicrobial Resistance Learning Site for Veterinary Students. Michigan State University, East Lansing, MI. 2011.
9. Dhillon, G.S.; Kaur, S; Pulicharla, R; Brar, S.K; Cledon, M; Verma, M; Surampalli, R.Y.  “Triclosan: Current Status, Occurrence, Environmental Risks and Bioaccumulation Potential.” Environmental Science Pollution Resource (2012) 19:1044-1065.

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