Enriched Groundwater Research Articles

Groundwater composition and recharge origin in the shallow aquifer of the Djerid oases, southern Tunisia: implications of return flow

Major ions and stable isotopes in groundwaters of the Plio-Quaternary shallow aquifer of the Djerid oases, southern Tunisia, were investigated to elucidate the origin of groundwater recharge and the mineralization processes. It has been demonstrated that the groundwater composition is mainly controlled by the water–rock interaction, the encroachment of brines from the Chotts and the return flow of irrigation waters. The isotopically depleted groundwater samples suggest that the recharge waters derive from an old palaeoclimatic origin. However, the enriched groundwater samples reflect the presence of evaporated recharge water. Furthermore, the large negative deuterium-excess values indicate the effect of secondary evaporation processes, probably related to the return flow of irrigation waters pumped from the underlying aquifer. Editor D. Koutsoyiannis; Associate editor E. Custodio Citation Tarki, M., Dassi, L. and Jedoui, Y., 2012. Groundwater composition and recharge origin in the shallow aquifer of the Djerid oases, southern Tunisia: implications of return flow. Hydrological Sciences Journal, 57 (4), 790–804.

Conversion, sorption, and transport of arsenic species in geological media

This work addresses the inter-conversion and sorption of inorganic As species in representative geological media. Through the sensitive quantification of As(III) and As(V) with liquid chromatography-inductively coupled plasma-mass spectrometry, and through integrated batch and column approaches, it is shown that natural media can either reduce or oxidize As species. Oxidation of As(III) to As(V) is shown in the Hanford sediment, while reduction of As(V) to As(III) is shown for the surface soil of Savannah River Site. Overall, the sorption distribution coefficient of As(V) onto geological media is much larger than that of As(III), and a reduction of the more sorptive As(V) to As(III) will lead to groundwater enrichment with As. Coupled with the different sorption behavior of As(III) and As(V), the inter-conversion of these species will strongly affect the geochemical cycling of redox-sensitive As in the subsurface. (C) 2012 Elsevier Ltd. All rights reserved.

The role of critical zone processes in the evolution of the Prairie Pothole Region wetlands

The Prairie Pothole Region, which occupies 900,000 km2 of the north central USA and south central Canada, is one of the most important ecosystems in North America. It is characterized by millions of small wetlands whose chemistry is highly variable over short distances. The study involved the geochemistry of surface sediments, wetland water, and groundwater in the Cottonwood Lakes area of North Dakota, USA, whose 92 ha includes the dominant wetland hydrologic settings. The data show that oxygenated groundwater interacting with pyrite resident in a component of surficial glacial till derived from the marine Pierre Shale Formation has, over long periods of time, focused SO42--bearing fluids from upland areas to topographically low areas. In these low areas, SO42--enriched groundwater and wetlands have evolved, as has the CaSO4 mineral gypsum. Sulfur isotope data support the conclusion that isotopically light pyrite from marine shale is the source of SO42-. Literature data on wetland water composition suggests that this process has taken place over a large area in North Dakota.

Hazardous concentrations of selenium in soil and groundwater in North-West India

Soil and groundwater samples were collected for bulk elemental analyses in particular for selenium (Se) concentrations from six agricultural sites located in states of Punjab and Haryana in North-West India. Toxic concentrations of Se (45–341 μg L −1) were present in groundwater (76 m deep) of Jainpur and Barwa villages in Punjab. Selenium enrichments were also found in top soil layers (0–15 cm) of Jainpur (2.3–11.6 mg kg −1) and Barwa (3.1 mg kg −1). Mineralogical analyses confirmed silicates and phyllosilicates as main components of these soils, also reflected by the high content of SiO 2 (40–62 wt.%), Al 2O 3 (9–21 wt.%) and K 2O (2.2–3.2 wt.%). Prevailing intensive irrigation practices in Punjab with Se enriched groundwater may be the cause of Se accumulation in soils. Sequential extraction revealed >50% Se bioavailability in Jainpur soils. Appearance of selenite was observed in some of the batch assays with soil slurries under reducing conditions. Although safe Se concentrations were found in Hisar, Haryana, yet high levels of As, Mo and U present in groundwater indicated its unsuitability for drinking purposes. Detailed biogeochemical studies of Se in sediments or groundwater of Punjab are not available so far; intensive investigations should be started for better understanding of the problem of Se toxicity.

Exploring sustainability of aquifers based on predictive modeling of sorption characteristics of arsenic enriched Holocene sediments in Bangladesh

Abstract The importance of accessing safe aquifers in areas with high As is being increasingly recognized. The present study aims to investigate the sorption and mobility of As at the sediment-groundwater interface to identify a likely safe aquifer in the Holocene deposit in southwestern Bangladesh. The upper, shallow aquifer at around 18 m depth, which is composed mainly of very fine, grey, reduced sand and contains 24.3 μg/g As, was found to produce highly enriched groundwater (190 μg/L As). In contrast, deeper sediments are composed of partly oxidized, brownish, medium sand with natural adsorbents like Fe- and Al-oxides; they contain 0.76 μg/g As and impart low As concentrations to the water (4 μg/L). These observations were supported by spectroscopic studies with SEM, TEM, XRD and XRF, and by adsorption, leaching, column tests and sequential extraction. A relatively high in-situ dissolution rate (Rr) of 1.42 × 10−16 mol/m2/s was derived for the shallower aquifer from the inverse mass-balance model. The high Rr may enhance As release processes in the upper sediment. The field-based reaction rate (Kr) was extrapolated to be roughly 1.23 × 10−13 s−1 and 6.24 × 10−14 s−1 for the shallower and deeper aquifer, respectively, from the laboratory-obtained adsorption/desorption data. This implies that As is more reactive in the shallower aquifer. The partition coefficient for the distribution of As at the sediment–water interface (Kd-As) was found to range from 5 to 235 L/kg based on in-situ, batch adsorption, and flow-through column techniques. Additionally, a parametric equation for Kd-As (R2 = 0.67) was obtained from the groundwater pH and the logarithm of the leachable Fe and Al concentrations in sediment. A one-dimensional finite-difference numerical model incorporating Kd and Kr showed that the shallow, leached As can be immobilized and prevented from reaching the deeper aquifer (∼150 m) after 100 year by a natural filter of oxidizing sand and adsorbent minerals like Fe and Al oxides; in this scenario, 99% of the As in groundwater is reduced. The deeper aquifer appears to be an adequate source of sustainable, safe water.

Reclaimed Water for Turfgrass Irrigation

Sustainable irrigation of turfgrass grown on coarse-textured soils with reclaimed water must avoid detrimental effects of soluble salts on plant growth and soil quality and groundwater enrichment of nitrogen (N) and phosphorus (P). The purpose of this study was (1) to investigate the effects of irrigating with municipal reclaimed water containing higher concentrations of soluble salts than potable water on turfgrass growth and quality and (2) to compare the effects of reclaimed and potable water on turfgrass assimilation and leaching of N and P. A sand-based medium plumbed to supply potable and reclaimed water and instrumented with lysimeters to collect leachate was planted with hybrid bermudagrass (Cynodon dactylon x Cynodon transvaalensis var. Tifsport) and creeping bentgrass (Agrostis stolonifera var. L-93). Both species produced high quality turfgrass with the reclaimed water. Although both grasses are moderately or highly salt tolerant when fully established, the bermudagrass growth and quality were reduced by the reclaimed water upon breaking dormancy, and its N use during this period was reduced. Continuous use of reclaimed water of the quality used in the study poses a potential soil Na accumulation problem. Both turfgrasses assimilated high amounts of N and P with minimal potential losses to groundwater.

Variations in the redox state of As and Fe measured by X-ray absorption spectroscopy in aquifers of Bangladesh and their effect on As adsorption

Groundwater enrichment with naturally occurring As is a very serious problem. In Bangladesh, many thousands of people are drinking such groundwater. Household well waters generally show a large variation of concentration of As even within a small village. This variation creates difficulty in the design of mitigation strategies. It was hypothesized that the concentration of As in each well is controlled by an adsorption–desorption equilibrium between sediment and groundwater. To verify the hypothesis, two factors are focused upon in this study: (i) speciation of As and Fe in the solid phase, and (ii) the adsorption properties of As(III) and As(V) to sediment. By this approach, it is possible to understand the variation of aqueous As in groundwater. Sediment core samples were collected from an As-enriched aquifer at Sonargaon, central eastern Bangladesh. The oxidation states of As and Fe in the sediments determined by X-ray absorption near edge structure (XANES) showed a distinct redox boundary below 5 m from the ground surface, whereas the peak of the concentration of dissolved As is observed below 15 m. The apparent distribution coefficient (Kd = Csolid/Csolution) of As(V) is always larger than that of As(III) at all the depths. Simulated concentrations of As in the groundwater obtained by multiplying the amount of P-extracted As and Kd-1 with consideration of the oxidation state of As is consistent with the depth profile of As in the groundwater. This suggests that the concentration of dissolved As is controlled by an adsorption–desorption equilibrium between sediment and groundwater. Variation in Kd is primarily controlled by the concentration of Fe oxyhydroxides, whereas surface area is also important for As(III). The discrepancy between the depth of the redox boundary and the peak of dissolved As is attributed to the difference in the abundance of P-extracted As rather than to a variation of Kd. The adsorption equilibrium model proposed in this study can be applied to the evaluation of the large variation in aqueous As concentration in groundwater from Holocene aquifers.

Model for the formation of arsenic contamination in groundwater. 1. Datong Basin, China

Mineral equilibria were analyzed in the system As-bearing rock-meteoric water. It was shown that carbonate rocks are the most probable source of As and Sr in the waters of the Datong Basin (People's Republic of China). The reason for groundwater enrichment in As is the shift of the equilibrium FeCO3 (siderite) + H2O = FeOOH(goethite) + CO2(g) + H2(g) to the left (toward siderite formation) owing to organic matter oxidation by atmospheric oxygen and an increase in the equilibrium partial pressure of CO2, while the Eh of the system remains below −0.30 ± 0.06 V.

Micropollutants: challenges in hydrogeology

In the 1990s, clofibric acid, a metabolite of lipid regulators, was found in the drinking water of Berlin, Germany (Heberer and Stan 1997). This drug made its way from households via wastewater treatment plants to surface waters and further into the waterworks’ wells by artificial groundwater enrichment and bank filtration. All over the world, hundreds of pharmaceuticals, hormones, additives of personal care products and detergents (collectively referred to as PPCP) have been found in wastewater, surface water and groundwater. Schwarzenbach et al. (2006) pointed to the contamination of water systems with these industrial and chemical compounds as “one of the key environmental problems facing humanity”. Most of them are present only at low concentrations in a range of pg l to ng l and therefore are termed micropollutants. In contrast, concentrations of macropollutants such as inorganic nitrogen, phosphate or BTEX (benzene, toluene, ethylbenzene and xylenes) are orders of magnitude higher (Schirmer and Schirmer 2008). The latter are relatively well knownwith respect to source, spatial extent, behaviour and remediation. Micropollutants, on the other hand, are ubiquitously present in complex mixtures and therefore much more difficult to assess (Schwarzenbach et al. 2006).

Treatment of arsenic rich waters by the HDS process

Arsenic contaminated waters are not uncommon; indeed from naturally occurring contaminated waters through to those that are a direct consequence of human activities such as mining, all are affecting the quality of water resources worldwide. The ever increasing demands on natural water resources mean that the effective control of this toxic contaminant is paramount and this is reflected in the ever increasing global legislation. There are currently three mechanisms by which arsenic is commercially treated in effluents. These are physical separation processes such as reverse osmosis, precipitation/adsorption processes, some of which are bacterially assisted, and a whole variety of ion exchange processes, again with some bacterial enhancement. The choice of treatment is not only driven by cost but by the chemistry of the water and the water quality standard to be met. In this study a very high arsenic enriched groundwater, containing in excess of 25,000 µg/L arsenic, was treated by a typical treatment method through a continuously operated pilot plant. In the treatment, iron III salts were added to the influent in order to form precipitates with the arsenic and to form an adsorptive surface that would assist with treatment of the enriched water. This addition of iron III salts for the removal of arsenic is common practice in the water treatment industry as the resulting iron III arsenates are highly stable. However, results from the pilot plant show that the process was further enhanced by the addition of small amounts of hydrogen peroxide. Hydrogen peroxide is a powerful oxidising reagent and assists in ensuring the complete conversion of any arsenic III to arsenic V that was then effectively removed in the pilot plant. After treatment residual arsenic levels of 10 µg/L were obtained compared to 68 µg/L without oxidation reagent addition.

Co-regulation of redox processes in freshwater wetlands as a function of organic matter availability?

Wetlands have important filter functions in landscapes but are considered to be the biggest unknowns regarding their element dynamics under global climate change. Information on sink and source function of sulphur, nitrogen, organic matter and acidity in wetlands is crucial for freshwater regeneration. Recent results indicate that redox processes are not completely controlled by the sequential reduction chain (that is electron acceptor availability) but that electron donor availability may be an important regulator. Our hypothesis was that only sites which are limited in their electron donor availability (low concentrations of dissolved organic carbon (DOC)) follow the concept of the sequential reduction chain. We compared the results of two freshwater wetland systems: 1) three forested fens within a boreal spruce catchment in a low mountain range in southern Germany (high DOC regime) and 2) three floodplain soils within a groundwater enrichment area in the Rhein valley in northwest Switzerland (low DOC regime). Micro scale investigations (a few cm 3) with dialyse chambers as well as soil solution and groundwater concentrations at the forested fens (high DOC regime) indicated simultaneous consumption of nitrate and sulphate with release of iron, manganese and methane (CH 4) as well as an enrichment in stable sulphur isotopes indicating a co-existence of processes attributed to different redox gradients. Soil and aquifer gas measurements down to 4.6 m at the groundwater enrichment site (low DOC regime and carbon limitation) showed extreme high rates of metabolism with carbon dioxide (CO 2) , dinitrous oxide (N 2O) and CH 4 concentrations reaching fifty, thirty and three times atmospheric concentrations, respectively. Simultaneously, groundwater oxygen (O 2) saturation was between 50 and 95%. We concluded that independent of DOC regime the sequential reduction chain was not a suitable concept in our systems. Instead of electron acceptor or donor availability micro site variability might explain the co-existence of redox processes within our sites.

A carbon-based method for estimating the wetness of forest surface soil horizons

The degree of wetness in forest surface soils has an effect on chemical and biological processes but is not easily measured. The high spatial variability in carbon (C) concentration creates high variability in water-holding capacity, and gravimetric water content is not informative. Local hydrology can create patchiness in soil moisture, with saturated soils often found near well-drained ones. When sampling to measure such factors as nitrification potential, it would be advantageous to have a simple metric that reflects the relative wetness of the soil. The relationship between C concentration (range 51.5–520.8 g·kg–1) and gravimetric water content was found to be linear for a set of 113 H- and A-horizon samples assumed to be at field capacity. The wetness ratio is defined as the actual water content of a sample divided by the water content predicted by the least squares regression equation based on C concentration (soil water content (kg·kg–1) = 0.080 + 0.0057 soil C concentration (g·kg–1)). Soil moisture retention curves were developed for a small number of samples in the range of 0 to about –10 kPa and showed that the equation predicted that water would be held at relatively high potential. In samples taken from 10 watersheds in the northeastern USA, wetness ratios between 1.25 and 3.1 were associated with soils identified in the field as ranging from wet to boglike. A median ratio of 0.49 was found in a watershed sampled after an extended dry period. At the Sleepers River Research Watershed, high wetness ratios were associated with a high soil calcium concentration, presumably from enriched groundwater. The ratio should be a useful measurement in watershed studies.

A Novel Reductive Dehalogenase, Identified in a Contaminated Groundwater Enrichment Culture and in Desulfitobacterium dichloroeliminans Strain DCA1, Is Linked to Dehalogenation of 1,2-Dichloroethane

A mixed culture dechlorinating 1,2-dichloroethane (1,2-DCA) to ethene was enriched from groundwater that had been subjected to long-term contamination. In the metagenome of the enrichment, a 7-kb reductive dehalogenase (RD) gene cluster sequence was detected by inverse and direct PCR. The RD gene cluster had four open reading frames (ORF) showing 99% nucleotide identity with pceB, pceC, pceT, and orf1 of Dehalobacter restrictus strain DSMZ 9455(T), a bacterium able to dechlorinate chlorinated ethenes. However, dcaA, the ORF encoding the catalytic subunit, showed only 94% nucleotide and 90% amino acid identity with pceA of strain DSMZ 9455(T). Fifty-three percent of the amino acid differences were localized in two defined regions of the predicted protein. Exposure of the culture to 1,2-DCA and lactate increased the dcaA gene copy number by 2 log units, and under these conditions the dcaA and dcaB genes were actively transcribed. A very similar RD gene cluster with 98% identity in the dcaA gene sequence was identified in Desulfitobacterium dichloroeliminans strain DCA1, the only known isolate that selectively dechlorinates 1,2-DCA but not chlorinated ethenes. The dcaA gene of strain DCA1 possesses the same amino acid motifs as the new dcaA gene. Southern hybridization using total genomic DNA of strain DCA1 with dcaA gene-specific and dcaB- and pceB-targeting probes indicated the presence of two identical or highly similar dehalogenase gene clusters. In conclusion, these data suggest that the newly described RDs are specifically adapted to 1,2-DCA dechlorination.

Analysis of Endocrine Disrupting Steroids: Investigation of Their Release into the Environment and Their Behavior During Bank Filtration

AbstractA reliable and sensitive analytical method for the determination of estrone (E1), 17β‐estradiol (E2), and the synthetic hormone 17α‐ethinylestradiol (EE2) has been established. Samples are concentrated using automated solid‐phase extraction and analysis is performed by liquid chromatography with detection by tandem mass spectrometry. Recoveries of all analytes were between 93% and 107%, and limits of quantification (LOQs) between 0.1 and 0.4 ng/L for purified sewage, and surface, ground, and drinking water, and between 1 and 2 ng/L in case of raw sewage. For the investigation of estrogen release into the environment and its behavior during sewage and surface water treatment, and during ground water recharge, samples from municipal waste water treatment plants (WWTPs), a surface water treatment plant, a bank filtration site, and a ground water enrichment (GWE) pond were analyzed. El was found in the raw waste water with an average concentration of 157 ng/L, whereas E2 and EE2 were found with mean concentrations of only 18 and 9 ng/L, respectively. Sewage treatment by municipal WWTPs affected a removal of EE2 (76%), El (92%), and E2 (94%). In the investigated surface water of Berlin, only E1 could be detected at concentrations around or below 1 ng/L. E2 and EE2 were not present in the Berlin surface water above the LOQ of 0.2 ng/L, respectively. Surface water treatment also leads to a significant removal of E1 (> 80%). In the ground water samples from the GWE site near Lake Tegel, only a few samples contained detectable concentrations of E1. These samples were collected from a shallow monitoring well located very close to the bank of the pond. Even a short distance between the bank and observation wells led to concentrations of El below the LOQ showing the potential of ground water recharge systems for the retention of estrogenic steroids depending on the environmental setting.

Occurrence of Endocrine-Disrupting and Other Wastewater Compounds during Water Treatment with Case Studies from Lincoln, Nebraska and Berlin, Germany

Research on the fate and transport of endocrine-disrupting compounds and other organic wastewater compounds released into the environment and their potential presence in drinking water is in its infancy. Studies conducted during the last decade in Lincoln, Nebraska, and Berlin, Germany, indicate that removal of less polar compounds probably can be obtained through bank filtration, ground-water enrichment, and additional drinking-water and wastewater treatment processes. Polar compounds, such as atrazine and some metabolites, occur in drinking water obtained from contaminated surface water or ground water, but at concentrations generally lower than those occurring in wastewater and surface water. The results of the studies also suggest that concentrations of nonpolar estrogenic compounds decrease during drinking-water pretreatment processes such as bank filtration and ground-water enrichment.

The flux of barium to the coastal waters of the southeastern USA: the importance of submarine groundwater discharge

Dissolved Ba concentrations in the inner shelf waters of the South Atlantic Bight (SAB) are two- to three-fold enriched in Ba when compared to Atlantic surface water. We determined that river input could account for about 25% of the observed enrichment. However, salty groundwaters are enriched in Ba by as much as an order of magnitude over calculated river water endmembers. The resultant input of Ba to the coastal environment, via enriched groundwater, is the likely source for the observed Ba enrichment on the inner shelf. The flux of Ba from the inner shelf to the ocean is 70 × 10 3 moles per day. The flux of Ba reaching the inner shelf from salty groundwaters ranges from 25 to 100 × 10 3 moles of Ba per day. Groundwater input of Ba appears to be much more important than river input for the Southeastern coast of the US.

Concomitant aerobic biodegradation of benzene and thiophene

AbstractThe concomitant aerobic biodegradation of benzene and thiophene was investigated in microcosm experiments using a groundwater enrichment culture. Benzene was biodegraded within 1 d, whereas thiophene could not be biodegraded as the sole source of carbon and energy. Some interesting phenomena were observed when both benzene and thiophene were present. In most cases, removal of thiophene was observed, and the removal occurred concomitantly with the biodegradation of benzene, suggesting that benzene was used as a primary substrate in the cometabolic biodegradation of thiophene. No biodegradation of the two compounds was observed for some combinations of concentrations, suggesting that thiophene could act as an inhibitor to benzene biodegradation. However, this effect could be overcome if more benzene was added to the microcosm. Residual concentrations of benzene and thiophene were observed in some microcosms and the data indicated that the biodegradation of the two compounds stopped when a critical threshold ratio between the concentrations of thiophene and benzene was reached. This ratio varied between 10 and 20. Results from modeling the biodegradation data suggested that thiophene was cometabolized concomitantly with the biodegradation of benzene and that the biodegradation may be described by a modified model based on a traditional model with an inhibition term incorporated.

CONCOMITANT AEROBIC BIODEGRADATION OF BENZENE AND THIOPHENE

The concomitant aerobic biodegradation of benzene and thiophene was investigated in microcosm experiments using a groundwater enrichment culture. Benzene was biodegraded within 1 d, whereas thiophene could not be biodegraded as the sole source of carbon and energy. Some interesting phenomena were observed when both benzene and thiophene were present. In most cases, removal of thiophene was observed, and the removal occurred concomitantly with the biodegradation of benzene, suggesting that benzene was used as a primary substrate in the cometabolic biodegradation of thiophene. No biodegradation of the two compounds was observed for some combinations of concentrations, suggesting that thiophene could act as an inhibitor to benzene biodegradation. However, this effect could be overcome if more benzene was added to the microcosm. Residual concentrations of benzene and thiophene were observed in some microcosms and the data indicated that the biodegradation of the two compounds stopped when a critical threshold ratio between the concentrations of thiophene and benzene was reached. This ratio varied between 10 and 20. Results from modeling the biodegradation data suggested that thiophene was cometabolized concomitantly with the biodegradation of benzene and that the biodegradation may be described by a modified model based on a traditional model with an inhibition term incorporated.

Determination of Clofibric Acid and N-(Phenylsulfonyl)-Sarcosine in Sewage, River and Drinking Water

Two polar compounds, the drug metabolite clofibric acid (2-(4)-chlorophenoxy-2-methyl propionic acid) and N-(phenylsulfonyl)-sarcosine, were detected as organic contaminants in groundwater samples from sewage farm areas near Berlin at maximum concentrations of 4 μg/l and 150 μg/l, respectively. Contaminations by these two compounds were also found in most of the drinking water samples collected from the 14 waterworks in the Berlin area. The maximum concentrations in drinking water samples were 270 ng/l for clofibric acid and 105 ng/l for N-(phenylsulfonyl)-sarcosine. The analytical results obtained correlate well with the percentage values of artificial groundwater enrichment and bank filtrate used by any particular water treatment plant in drinking water production. Thus, it can be assumed that both polar contaminants commonly leach into drinking water and are not eliminated by the drinking water treatment used by the Berlin waterworks. Positive findings in screening analyses of surface water samples outside Berlin as, for example, the river Danube in Germany and the river Po in Italy indicate that the occurrence of clofibric acid and N-(phenylsulfonyl)-sarcosine in environmental water samples is not just a local phenomenon.

Identification of Metabolites from the Biological Transformation of the Nonionic Surfactant Residue Octylphenoxyacetic Acid and Its Brominated Analog

The aerobic biological transformation of octylphenoxyacetic acid (OP1EC) and its brominated analog (BrOP1EC) by groundwater enrichment cultures was studied, and persistent metabolites were identified by GC/MS. OP1EC is a representative of the class of alkylphenol ethoxycarboxylates (APEC), formed from alkylphenol polyethoxylate nonionic surfactants during sewage treatment. BrOP1EC is a byproduct formed during chlorine disinfection in the presence of bromide. The metabolite 2,4,4-trimethyl-2-pentanol was detected in stoichiometric quantities in OP1EC-metabolizing enrichment cultures, representing the intact alkyl side chain as a tertiary alcohol. BrOP1EC was transformed by the OP1EC-utilizing cultures only if OP1EC was simultaneously metabolized, suggesting a cometabolic mechanism of transformation. Brominated intermediates were also detected: brominated octylphenol and a compound tentatively identified as 2-aminomethoxy-3-bromo-5-(1,1,3,3-tetra- methylbutyl)phenol.