Research Effect of Surfactants on the Survival and Sorption of Viruses DEVAMITA CHATTOPADHYAY,† S A N D I P C H A T T O P A D H Y A Y , * ,† WILLIAM G. LYON,† AND JOHN T. WILSON‡ ManTech Environmental Research Services Corporation, 919 Kerr Research Drive, Ada, Oklahoma 74820, and United States Environmental Protection Agency, National Risk Management Research Laboratory, Subsurface Protection and Remediation Division, 919 Kerr Research Drive, Ada, Oklahoma 74820
There is an increasing concern about the protection of groundwater from contamination by enteric viruses and the prevention of outbreaks of waterborne diseases. Knowledge of survivability and transport of viruses from their point of origin is necessary to determine their potential effects on the neighboring groundwater systems. The distribution of virus is, in turn, dependent on the physical and chemical compositions of the surrounding soil and subsurface systems. For the present study, we have determined the effects of different surfactants (cationic, anionic, nonionic, and biological) and natural organic matter (NOM) on bacteriophages. Results indicated that surfactants and NOM adversely affect phage survival in binary systems, with surfactants being the most harmful. Studies with ternary systems also showed that the presence of surfactants reduced sorption of phages on sorbents either by occupying available sorption sites on the sorbent material or by displacing the sorbed phages from the sorbent surface. Water contact angles of the selected phages and different sorbent surfaces have been measured. Experimental data demonstrated that the sorption of hydrophobic viruses was favored by hydrophobic sorbents, while the sorption of hydrophilic viruses was favored by hydrophilic sorbents.
Introduction Septic systems, which are used in approximately 24.1% of all United States households (1), are the most voluminous and the most numerous point sources (approximately 24.7 million) of all the effluents discharged to groundwater in United States. Several recent reviews (2-5) have indicated that entry, survival, and transport of pathogenic microorganisms present in septic systems in groundwater were responsible for large outbreaks of waterborne diseases; therefore, effluents from septic tanks and cesspools are health risks. Considerable effort has been made to understand the fate of these pathogenic microorganisms in soil in order to estimate the impact of a potential septic system discharge * Corresponding author present address: Battelle Memorial Institute, Environmental Restoration Dept., 505 King Ave., Columbus, OH 43201; phone: (614)424-3661; fax: (614)424-3667; e-mail:
[email protected]. † ManTech Environmental Research Services Corporation. ‡ United States Environmental Protection Agency. 10.1021/es0114097 CCC: $22.00 Published on Web 08/22/2002
2002 American Chemical Society
on a nearby drinking water system. The concentration of a pathogen at any distance from the point source depends not only on the survival of the virus in that particular soil system but also on the amount of viruses sorbed on the soil particles. On the basis of the above considerations, the present study determined the survival of different model viruses under different conditions and also measured the amount of sorption of these viruses on different sorbents. Bacteriophages were selected as model viruses as they serve as ideal indicators of viral pollution and models for enteroviruses in natural waters (6). Clay minerals, which are a major inorganic constituent of soil, have been selected as model sorbents since their high surface area affects sorption of microorganisms in the soil system. Additionally, sorption of these bacteriophages on different iron oxides has also been studied. Selection of iron oxides was based on the fact that iron is a major constituent of the lithosphere (approximately 5.1%), and its average content in soils is estimated at 3.8% (7). The selected sorbents are expected to represent the probable subsurface materials in aquifers that are likely to receive leachate effluents from septic tanks. Surfactants are found commonly in septic tank effluents as well as in soil and subsurface environment as they are present in a wide range of consumer products. Because of the ubiquitous presence of surfactants in the subsurface system, we have studied the survival of the selected bacteriophages in the presence of different chemical and biological surfactants. We have also measured the effect of these surfactants on the amount of bacteriophages sorbed on sorbents. Humic materials, which constitute the greatest proportion of natural organic matter (NOM), have also been included in this study to determine their effect on bacteriophages. Pieper et al. (8) have studied the effect of both organic matter and surfactant on the sorption of phages on iron oxides and have found that they adversely affect the sorption capacity of the iron oxides toward the phages. Modern laundry detergents generally contain approximately 20% surfactant by weight. The active portion of detergents is normally composed of both anionic and nonionic surfactants. Linear alkyl benzene sulfonates (LAS) are the most frequently employed synthetic anionic surfactants. In 1991, Richtler and Knaut (9) estimated that the production of LAS amounted to 1,040,000 t yr-1 in the United States, Japan, and Western Europe. As per the U.S. International Trade Commission (10) report, 842 million kg of nonionic surfactants was produced in the United States in 1991 with the most widely used being linear alcohol ethoxylates (AE), which represented approximately 39% of all nonionic surfactants produced. Cationic surfactants, distearyl dimethylammonium chloride and ditallow (C16-C18) dimethylammonium chloride, are widely used as anti-static agents and fabric softeners; in 1983, Lewis and Wee (11) estimated the yearly usage level to be about 24.5 million kg in the United States. These surfactants tend to accumulate in ecosystems and can significantly affect viral transport to drinking water wells. Representative members of the above three groups of surfactants were chosen for the present study. Studies have also been conducted to provide estimates of surfactant and NOM concentrations in wastewater streams. On the basis of the amount of laundry detergent used and the wastewater flow rate, Lee et al. (12) calculated the usage rate of laundry detergent for an average household, which was 89.25 gal day-1. Prats et al. (13) estimated the amount of anionic surfactants and nonionic surfactants in a conVOL. 36, NO. 19, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Physical Characteristics of Selected Substrates
compositiona
mineral
hectorite (Na-satd, Na1.59[Mg4.60Li1.39Ti0.01]‚
