REVIEWS AND ANALYSES Behavior and Transport of Microbial Pathogens and Indicator Organisms in Soils Treated with Organic Wastes

In a critical review of pathogen and indicator-organism transformations and transport from land areas receiving organic wastes, microbial die-off was described assuming first-order kinetics. First-order die-off rate constants (k) were calculated from the literature data for various pathogens and indicator organisms. For indicator organisms average die-off.rates were 1.14 day-’ (0.08-9.1) for fecal coliforms, and 0.41 day-’ (0.05-3.87 day-’) for fecal streptococci. For pathogens, the average die-off rates were 1.33 day-’ (0.21-6.93) for Salmonella, 0.68 day-’ (0.62-0.74 day-~) for Shigella sp., and 1.45 day-’ (0.04-3.69 day-’) for viruses, respectively. Die-off rates increased approximately two times with a 10°C rise in temperature ($-30°C). Microbial die-off increased with decrease in soil moisture and was minimum in a pH range of 6-7. Correction factors were presented to adjust the k values for the changes in temperature, moisture, and pH. Retention of pathogens and indicator organisms by soil particles was described as. suming a linear isotherm. Retention of microorganisms increased with an increase in clay content of the soil. Major transport processes reviewed were leaching and surface runoff for land areas receiving animal wastes, and pastures and rangeland watersheds where animals distribute waste directly on the land. Some of the important research needs identified include (i) mechanisms involved in the retention of bacteria and viruses by the soil; (ii) measurement of retention coefficients for some important pathogens and indicator organisms, as a function of physico-chemical properties of soil; (iii) processes involved in the transport of bacteria and viruses ’ Paper no. 6448 of the Journal Series of the North Carolina Agric. Res. Serv., Raleigh. This research was supported in part by the United States Environmental Protection Agency, grant no. R-805011-0-1-0. Received 26 Jan. 1980. 2 Assistant Professor, Univ. of Florida, IFAS Agricultural Research & Education Center, P.O. Box 909, Sanford, FL 32771; Assistant Professor, Dep. of Geoscience, New Mexico Institute of Mining and Technology, Socorro, NM 81801; and Professor, Dep. of Biol. and Agric. Eng., North Carolina State Univ., Raleigh, NC 27650, respectively. along with the percolating water or in runoff water; and (iv) extensive testing of available models. Additional Index Words: Microbial die-off, pathogens, viruses, soil retention, nonpoint source, animal wastes, runoff water quality. Reddy, K. R., R. Khaleel, and M. R. Overcash. 1981. Behavior and transport of microbial pathogens and indicator organisms in soils treated with organic wastes, J. Environ. Qual. 10:255-266. Nonpoint source pollution of surface waters is a contribution of several land-use activities. The major pollutants include soluble N, P, and C; pesticides; sediment and sediment-associated N, P, and C; and pathogens. The quality of surface waters is dependent on the availability of these pollutants at the soil surface during a rainfall event. Often the constituents in animal wastes that most frequently violate stream quality standards during runoff are bacterial indicators. This phenomenon is somewhat artificial since the stream standards are established relative to bacteria of human, rather than animal, origin. Pathogenic organisms have long been associated with animals and animal wastes. A number of pathogenic organisms are known to be involved in transmitting diseases through animal waste. These include members of the Salmonella, Mycobacterium, Erysipelothrix, Leptospira, and Clostridium genera, as well as Bacillus anthracis, FMD virus, enteroviruses, helminths, etc. (Ellis and McCalla, 1976). There are approximately 100 diseases that can be transmitted from animals to man (Diesch, 1970). Recently, several review papers have appeared describing the disease hazards, and bacterial and J. Environ. Qual., Vol. 10, no. 3, 1981 255 viral pathogens associated with the land application of organic wastes (Elliott and Ellis, 1977; Burge and Marsh, 1978; Menzies, 1977; Morrison and Martin, 1976). These reviews, however, do not evaluate the pathogen transformations in the soil in relation to nonpoint source pollution of surface waters. The availability of pathogens and indicator organisms at the soil surface during a rainfall event is dependent on several processes and factors. The most important process is the die-off rate (or survival rate) of the pathogens in the soil-waste system. Fecal contamination of the soil and subsequent entry of pathogens into a water supply is dependent on survival of the organisms during residence time in the soil and likelihood of’ being washed out by storm water runoff. A schematic presentation of the pathogen cycle in the land areas receiving organic wastes is shown in Fig. 1. Comprehensive information on survival periods of several pathogens in the soil-plant-waste water system is presented by Parson et al. (1975) and Morrison and Martin (1976). The survival periods for these organisms range from 30 min to several years. A number of factors are known to influence the survival of pathogens and indicator organisms in a soil-waste system: waste pretreatment, moisture, temperature, sunlight, pH, antibiotics, toxic substances, competitive organisms, available nutrients, organic matter, method and time of application of waste, and soil type. Another important process that controls the availability of the organisms in the soilwaste system is the soil adsorption or retention of organisms. Retention of the organisms is enhanced when clay is present in the soil. The most widely accepted bacterial indicators of fecal pollution in water have been the coliform group (Am. Public Health Assoc., 1971). Fecal streptococci, have also been used as indicators. The ratio of fecal coliforms to fecal streptococci (FC/FS) was suggested as a possible tool for evaluating waste voided by man and lower animals. A FC/FS ratio > 4.0 indicates a human waste source; <0.7, a lower animal source; and between 0.7 and 4.0, a mixed source (Table 1). The objectives of this study were (i) to develop a conceptual model for nonpoint source contributions of bacteria based on the state-of-the-art approach; (ii) to estimate kinetic rate coefficients for die-off from the data reported in the literature; (iii) to evaluate mechanisms pathogen-retention in soil particles; (iv) to discuss the CELLS ORGAN IC HASTE | PATI~ENS RETENT 1 ON DEAD ~ DIEOFF ~ (BACTERIA ~ BY SOIL WATER STE SED IHENT E~CT~LE PARTICLE ASS~ATED