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Several sample preparation methods for extracting high-quality DNA for PCR were evaluated. For Escherichia coli, Xtra Amp tube, Isocode paper, Instagene matrix, and PrepMan matrix methods were all suitable. For Cryptosporidium parvum, Xtra Amp and Instagene methods were suitable.

Researchers describe a technique for identifying E. coli O157 in water using immunomagnetic beads with a monoclonal anti-O157:H7 IgG combined with a polyclonal anti-O157:H7 IgG with an electrochemiluminescent label attached. This strain of E. coli is usually transmitted in contaminated meat, but it can also contaminate water.

Research has been conducted in an effort to establish methods to effectively detect the presence of Cryptosporidium parvum, a protozoan parasite that causes cryptosporidosis. The sat flotation method has been discovered to result in the highest percentages of C. parvum recovery when compared to seven other concentration and purification methods. C parvum oocycts are believed to be waterbase, but can also be found in contaminated soil and bovine feces. The salt flotation method has ben found to be the most effective and suitable process for routine detection of C. parvum oocysts in a variety of environmental matrices.

A model is proposed for describing pesticide - substrate bioavailability and rates of biodegradation in soil. The model accounts sorption to soil surfaces, diffusion into the internal matrix of soil organic matter or aggregates, and microbial growth. Rates of sorption and diffusion are approximated by first-order kinetics while microbial growth is approximated by Monod kinetics. Model verification was performed using 2,4-D (2,4-dichlorophenoxyacetic acid) degradation data from high and low organic matter soils inoculated with pure cultures of 2,4-D degrading bacteria. Estimates of sorption, diffusion, and Monod constants were obtained sequentially by fitting the defining differential equations to the data using nonlinear regression techniques. Independent estimates of initial biomass ([X.sub.0]) and growth yield (Y) were required, although [X.sub.0] could be approximated from the number of colony-forming units assuming a bacterial weight of 0.1 pg [cell.sup.-1]. The model could account for the partitioning of 2,4-D between soluble and sorbed phases and provided estimates of the Monod constants, [[Mu].sub.max] and [K.sub.s], which were generally consistent with values previously determined in pure culture. In conjunction with pest toxicology data, the model may be useful in predicting the time between application and loss of efficacy (i.e., window of efficacy) for biodegradable pesticides.

A model was developed for describing rates of pesticide-substrate biodegradation, accounting for bioavailability and microbial growth. The model was used to simulate losses of efficacy for soil-applied pesticides. The model requires rate constants for rapid sorption - desorption to and from soil surfaces ([k.sub.1]/[k.sub.-1] = [K.sub.d1]); diffusion into and out of soil aggregates-organic matter particles ([k.sub.2]/k.sub.-2] = [K.sub.d2]); microbial growth [yield (Y), maximum growth rate ([[Mu].sub.max]), half-saturation growth constant ([K.sub.s]), and initial biomass concentration initial mass of substrate ([S.sub.0]); and gravimetric water content ([[Theta].sub.g]). Simulations of microbial growth and substrate depletion were conducted assuming no sorption (aqueous solution), sorption to soil surfaces only, and sorption in conjunction with diffusion. The time required to achieve a soil solution concentration of 1 [[micro]gram] [mL.sup.-1] was defined as a hypothetical loss of efficacy (L[E.sub.1]). Certain relationships were consistently observed, regardless of sorption or diffusion: L[E.sub.1] was found to be related to [K.sub.s] linearly, to [X.sub.0] logarithmically, to [[Mu].sub.max], geometrically, and to initial pesticide-substrate concentration ([S.sub.0]) nonlinearly. Sorption to soil surfaces resulted in decreased equilibrium soil solution concentration ([S.sub.e]), depending on the magnitude of [[Theta].sub.g] and [K.sub.d1]. Rates of biodegradation-growth were a function of [S.sub.e], as opposed to total (soluble - sorbed) concentration. Sorption coupled with diffusion decreased both [S.sub.e] and time-dependent availability, resulting in slower rates of biodegradation. In general, larger values of [S.sub.0] resulted in faster rates of biodegradation, i.e., decreased the time required a loss of efficacy.

The growth kinetics of two bacterial strains, MI and 155, were investigated to determine the conditions neccessary for successful biodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in soil. The kinetics of degradation of 2,4-D in soil was consistent with findings in pure culture. Higher degradation rates were obtained in low-organic-matter soils. This was correlated to the availability of 2,4-D as a function of its solubility and retention in soil particles. Available solubilized 2,4-D is preferentially degraded, followed by desorbed and soluble 2,4-D.

The kinetics of 2,4-dichlorophenoxyacetic acid (2,4-D) degradation among seven strains of bacteria were studied. The values for half saturation growth constants ranged from 10 micromolar to 154 micromolar, while the estimates of maximum growth rates in terms of doubling times ranged from 3.5 hours to 2.2 hours. These and other data suggests that a kinetic diversity for 2,4-D degradation exists amongnaturally occuring microbial populations. Such diversity may be useful in the selection of inoculant strains for the effective degradation of specific environmental pollutants.

Research study is conducted to compare the attachment of fecal coliforms to different soils and soil fractions and to assess the effect of bovine manure on fecal coliform attachment to soil and soil functions. It is found that the attachment to the coated sand particle is similar to the attachment to silt and clay.

A study to assess the effect of dilute bovine manure versus that of no manure on attachment and subsequent detachment of Cryptosporidium parvum oocysts to soil is conducted. The results indicate that the oocyst attachment to soil is substantially affected by bovine manure in a complex manner and has implications for how oocyst might be transported through or over soils.

Weekly surveys of stream water was conducted in the metropolitan Baltimore area for the prevalence of potentially pathogenic Escherichia coli strains through the use of PCR for the tir and stx1 and stx2 genes are presented. The results reveal that pathogenic Escherichia coli are continually deposited into a variety of stream habitats and suggest that this organism might be a permanent member of the gastrointestinal microflora of humans and animals in the metropolitan Baltimore area.