Treating soil solution samplers to prevent microbial removal of analytes.

Soil microorganisms colonizing soil water sampling devices (lysimeters) reduced concentrations of biodegradable organic chemicals, including 2,4-dichlorophenoxyacetic acid methyl ester, alachlor, methyl m-chlorobenzoate, and metolachlor as water entered through porous ceramic cups. In some cases, losses exceeded 99%. Additions of either a biocide (sodium hypochlorite) or a bacteriostat (copper salt) prevented microbial activity so that concentrations of test chemicals inside lysimeters equaled those outside. Field studies further indicated that treating lysimeters with a copper salt effectively prevented microbial activity. Thus, chemically treating soil water samplers could improve the accuracy of soil water data for a wide variety of analytes, including environmentally important organics, such as pesticides and industrial wastes, and inorganics, such as ammonia and nitrate.

Initial test of the benchmark chemical approach for predicting microbial transformation rates in aquatic environments.

Using 2,4-dichlorophenoxyacetic acid methyl ester (2,4-DME) as a benchmark chemical, we determined relative pseudo-first-order rate coefficients for the butoxyethyl ester of 2,4-dichlorophenoxyacetic acid (2,4-DBE), methyl parathion, and methyl-3-chlorobenzoate in a diversity of microbial samples, including water, sediment, biofilm, and floating microbial mats collected from a laboratory mesocosm as well as from streams, lakes, and wetlands in Georgia and Florida. The decreasing order of reactivity for relative microbial transformation rates was 2,4-DBE > 2,4-DME > methyl-3-chlorobenzoate > methyl parathion. Half-lives of the chemicals varied about 60-fold depending on the chemical and microbial sample. Relative rate coefficients, however, typically varied only about threefold for field-collected samples. Relative rate coefficients determined with samples from a laboratory mesocosm were consistently low compared with the field sample data. Overall, the data indicated that microbial transformation rates of a chemical can be satisfactorily inferred for a wide variety of microbial habitats-such as water, biofilm, or a sediment-on the basis of its transformation rate relative to that of an appropriate benchmark chemical by using a single type of microbial sample.

Prediction of substrate removal rates of attached microorganisms and of relative contributions of attached and suspended communities at field sites.

A mathematical model composed of a direct proportionality relationship between bulk water velocities and field-determined second-order microbial transformation rate coefficients, and the relative rate coefficient of a benchmark chemical, was developed for estimating the substrate removal rates of rapidly degraded chemicals by attached organisms in shallow (<1 m deep) aquatic ecosystems. Data from 31 field experiments involving the addition of 2,4-dichlorophenoxyacetic acid methyl ester (2,4-DME) in nine field areas were used to determine a field-derived second-order rate coefficient for microbial transformation of the ester. By using 2,4-DME as a benchmark chemical, the model was used to predict microbial transformation rates of the butoxyethyl ester of 2,4-dichlorophenoxyacetic acid (2,4-DBE) at five other field sites. The predicted half-lives of 2,4-DBE varied 1,500-fold and were within about a threefold range or less of the measured half-lives. Under conditions of mass transport limitation, the contributions of attached microorganisms relative to total microbial activities at various field sites were related to the ratio of water velocity, U, and depth, D, showing that historical definitions of ecosystems according to flow and depth characteristics are also valid for describing the process-related structure of ecosystems. An equation was developed for predicting the relative contributions of attached and suspended communities with values of U and D for lotic and lentic ecosystems. On the basis of this equation, attached microorganisms were expected to be insignificant in deep lentic ecosystems and suspended microorganisms were expected to be insignificant in shallow lotic systems for the same process carried out by both populations. Neglecting epiphytic microorganisms, both suspended and attached organisms were expected to be significant in wetlands.