Fate of Benzene in a Stratified Lake Receiving Contaminated Groundwater Discharges from a Superfund Site

Abstract

Predicting the fate of benzene in aquatic environments, and estimating corresponding human exposures, is critically dependent on knowledge of this carcinogen's biodegradation rate under the site-specific conditions. We used three approaches for quantifying this key fate process: (1) shortterm (hours) observations of benzene loss in laboratory incubations of representative water samples, (2) wholelake benzene mass balance studies, and (3) modeling of the temporal evolution of benzene vertical profiles in the lake. Our field site, the Halls Brook Holding Area (HBHA), continuously receives benzene input (about 20 µM or 1.5 ppm) into its anoxic hypolimnion via discharge of saline groundwater from an adjacent Superfund site (Industri-Plex in Eastern Massachusetts.) Using summertime, lake water samples in the laboratory, we found benzene was degraded in three metalimnion samples at rates between 1 and 2.5 d -1 . An epilimnion sample yielded a similar result, but no degradation was observed in another epilimnion sample. Losses were e0.04 d -1 in a sulfate-rich hypolimnion sample. Since benzene loss could be inhibited by filtration or with a mixture of poisons and antibiotics, it was apparently being biodegraded. In the whole-lake mass balance studies of benzene, it was found that approximately 80% of the benzene entering the lake was degraded during the water's residence in the lake. Vertical distributions of benzene in the HBHA water column indicated that the chief sink of benzene was located in the metalimnion. A twomonth progression of summertime profiles of benzene concentration vs depth was fitted well using a dynamic model, CHEMSEE, and assuming that the only sinks were epilimnetic flushing, water-to-air exchange, and biodegradation in a 0.4 m-thick metalimnetic layer at 2 d -1 . The biodegradation rate derived from such whole-system study appears more dependable than rates deduced from grab samples, and we suggest that we must learn to predict these intact-system rates.

Novel hopanoid cyclases from the environment

“…Lake Mishwam is methanogenic. A sharp density contrast maintains permanently anaerobic conditions and stratification is preserved during all but the most extreme weather systems (Wick et al ., 2000). Methane is oxidized at the chemocline boundary, and aerobic methanotrophs (γ‐ and α‐proteobacteria) are found in the water column (M. Fisher, pers.…”

“…It also is possible that these samples contain particulate material mixed in from deeper waters. Although the lake stratification is extreme (surface water residence time a few days, deep water residence time > 100 days; Wick et al ., 2000) some cross‐chemocline mixing must occur. Quantitative PCR and comparisons between surface and deep waters may resolve this question in the future.…”

NEREUS: engineering concept for an underwater mass spectrometer

“…6. Bottom water known to be anoxic and to contain methane [24] was collected for this experiment in a BOD (biochemical oxygen demand) bottle from the Mishawum Lake (also known as Halls Brook Storage Area) in the Aberjona River watershed, north of Boston, MA, USA. Intermediate points in Fig.…”

Mixing and Transport

“…By comparing the model predictions with data from a lake and reservoir in California, the researchers showed that the maximum half-life of MTBE is less than forty days under calm conditions and approximately six days when the average wind speed is more than ten miles per hour. To investigate the fate of benzene in a stratified lake located next to a superfund site, Wick et al (2000) used three approaches: shortterm (hours) observations of benzene decay under laboratory conditions, entire-lake benzene mass balance calculations, and temporal evaluation of benzene vertical profiles modeling in the lake. The calculations showed that the metalimnion was the main sink for the benzene, and about 80% of the benzene received by the lake was degraded during the water residence.…”