Metabolism and body-burden of PCBs in lactating dairy cows.

This paper uses data from a detailed 4 month PCB mass balance study on lactating cows fed a naturally contaminated background diet to quantify the metabolism and body-burdens of a range of PCB congeners. Dietary intake fluxes and milk and faecal output fluxes reported previously are combined with subcutaneous fat and blood PCB concentrations and with data from tissue/organ samples from a slaughtered animal to estimate the degree of metabolism within the cow. A total body burden is derived, showing that fat deposits account for approximately 98% of total PCB present in the lactating cow. The daily intake through feed (ng day-1) accounted for between 0.9 and 1.5% of the total body burden for persistent congeners (e.g. PCB 153) and up to 43% for those congeners which are readily metabolised (e.g. PCB 52). Detailed balances for a range of tri- to octa-chlorinated PCBs are presented and clearly demonstrate that many congeners are metabolised effectively by lactating dairy cows (e.g. PCB 149) whilst others are efficiently transferred to human dairy food products. An approach to predicting the degree of metabolism for individual PCB congeners is presented which gives good agreement with observations.     

Polychlorinated biphenyls in digested UK sewage sludges

Twelve sewage sludges from rural, urban and industrial waste water treatment works in north west England were analysed for polychlorinated biphenyls by capillary GC-ECD. The total polychlorinated biphenyl content ranged between 106 to 712 μg/kg, with a mean of 292 μg/kg. Di- and penta-chlorinated congeners made the greatest contribution to the ΣPCB concentrations at most sites. The 6 IUPAC congeners were found in the following order of abundance, 101>180>153>138>52>28. Industrial inputs would appear to influence levels of ΣPCB in the sludge.

If these sludges were ploughed into arable land at typical rates only a slight elevation in soil ΣPCB levels would result. Alternatively, if the same quantity of sludge were applied to the surface of pasture grassland, significant elevations in the potential transfer of PCBs to grazing livestock may result.     

Conceptual and numerical model of uranium(VI) reductive immobilization in fractured subsurface sediments

A conceptual model and numerical simulations of bacterial U(VI) reduction in fractured subsurface sediments were developed to assess the potential feasibility of biomineralization at the fracture/matrix interface as a mechanism for immobilization of uranium in structured subsurface media. The model envisions flow of anaerobic groundwater, with or without acetate as an electron donor for stimulation of U(VI) reduction by dissimilatory metal-reducing bacteria (DMRB), within mobile macropores along a one-dimensional flow path. As the groundwater moves along the flow path, U(VI) trapped in the immobile mesopore and micropore domains (the sediment matrix) becomes desorbed and transferred to the mobile macropores (fractures) via a first-order exchange mechanism. By allowing bacterial U(VI) reduction to occur in the mesopore domain (assumed to account for 12% of total sediment pore volume) according to experimentally-determined kinetic parameters and an assumed DMRB abundance of 10(7) cells per cm3 bulk sediment (equivalent to 4 mg of cells per dm3 bulk sediment), the concentration of U(VI) in the macropore domain was reduced ca. 10-fold compared to that predicted in the absence of mesopore DMRB activity after a 6-month simulation period. The results suggest that input of soluble electron donors over a period of years could lead to a major redistribution of uranium in fractured subsurface sediments, converting potentially mobile sorbed U(VI) to an insoluble reduced phase (i.e. uraninite) in the mesopore domain that is expected to be permanently immobile under sustained anaerobic conditions.     

Non-aqueous phase liquid spreading during soil vapor extraction

Many non-aqueous phase liquids (NAPLs) are expected to spread at the air-water interface, particularly under non-equilibrium conditions. In the vadose zone, this spreading should increase the surface area for mass transfer and the efficiency of volatile NAPL recovery by soil vapor extraction (SVE). Observations of spreading on water wet surfaces led to a conceptual model of oil spreading vertically above a NAPL pool in the vadose zone. Analysis of this model predicts that spreading can enhance the SVE contaminant recovery compared to conditions where the liquid does not spread. Experiments were conducted with spreading volatile oils hexane and heptane in wet porous media and capillary tubes, where spreading was observed at the scale of centimeters. Within porous medium columns up to a meter in height containing stagnant gas, spreading was less than ten centimeters and did not contribute significantly to hexane volatilization. Water film thinning and oil film pinning may have prevented significant oil film spreading, and thus did not enhance SVE at the scale of a meter. The experiments performed indicate that volatile oil spreading at the field scale is unlikely to contribute significantly to the efficiency of SVE.     

Estimation of PCDD/F distribution and fluxes in the Venice Lagoon,Italy: combining measurement and modelling approaches

The available experimental information on the occurrence of PCDD/Fs in the Venice Lagoon, Italy, was compiled and used to calculate fugacities for the environmental compartments of sediment, suspended particulate matter (SPM), water and air and then used to estimate fugacity ratios and assess the likely net direction of flux between media. The bottom sediment: SPM fugacity ratios for different PCDD/Fs indicate conditions close to equilibrium, suggestive of the close coupling of SPM with re-suspended sediment. Sediment/water and the sediment/air fugacity ratios suggest that net flux directions vary depending on the congener and the location within the lagoon. Net sediment-water-air movement (i.e. re-mobilisation/volatilisation) is suggested for the lighter congeners from the industrial canals, where the highest PCDD/F concentrations in the lagoon occur. The tendency to volatilise increases with decreasing congener molecular weight. In contrast, net deposition (air-water-sediment) appears to be occurring for the heaviest (hepta- and octa-) substituted PCDD/Fs. OCDF represents a marker of the industrial district of the lagoon, decreasing in concentration and as a fraction of total PCDD/Fs with increasing distance. The fugacity-based quantitative water air sediment interaction (QWASI) mass-balance model was applied to the central part of the lagoon. The key parameters for the determination of the model output, identified by a sensitivity analysis, were: the sediment active depth, the sediment re-suspension and deposition rates, and the total input of PCDD/Fs to the system. The QWASI model also indicates the tendency for the lighter PCDD/Fs to be released from surface sediment to the water column.     

Summer-time distribution of air pollutants in Sequoia National Park, California

Concentrations of air pollutants were monitored during the May November 1999 period on a network of forested sites in Sequoia National Park, California. Measurements were conducted with: (1) active monitors for nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3); (2) honeycomb denuder/filter pack systems for nitric acid vapor (HNO3), nitrous acid vapor (HNO2), ammonia (NH3), sulfur dioxide (SO2), particulate nitrate (NO3-), ammonium (NH4+), and sulfate (SO4(2-)); and (3) passive samplers for O3, HNO3 and NO2. Elevated concentrations of O3 (seasonal means 41-71 ppb), HNO3 (seasonal means 0.4-2.9 microg/m3), NH3 (seasonal means 1.6-4.5 microg/m3), NO3 (1.1-2.0 microg/m3) and NH4+ (1.0-1.9 microg/m3) were determined. Concentrations of other pollutants were low. With increasing elevation and distance from the pollution source area of O3, NH3 and HNO3 concentrations decreased. Ammonia and NH4+ were dominant N pollutants indicating strong influence of agricultural emissions on forests and other ecosystems of the Sequoia National Park.     

Radiocarbon content of synthetic and natural semi-volatile halogenated organic compounds

Some halogenated organic compounds, such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polybrominated diphenyl ethers (PBDEs), have been suggested to have natural sources but separating these compounds from their commercially synthesized counterparts is difficult. Molecular-level 14C analysis may be beneficial since most synthetic compounds are manufactured from petrochemicals (14C-free) and natural compounds should have "modern" or "contemporary" 14C levels. As a baseline study, we measured, for the first time, the 14C abundance in commercial PCB and PBDE mixtures, a number of organochlorine pesticides, as well as one natural product 2-(3',5'-dibromo-2'-methoxyphenoxy)-3,5-dibromoanisole. The latter compound was isolated from a marine sponge and is similar in structure to a PBDE. All of the synthetic compounds were 14C-free except for the pesticide toxaphene. which had a modern 14C abundance, as did the brominated natural compound. The result for toxaphene was not surprising since it was commercially synthesized by the chlorination of camphene derived from pine trees. These results suggest that measuring the 14C content of halogenated organic compounds may be quite useful in establishing whether organic compounds encountered in the environment have natural or synthetic origins (or both) provided that any synthetic counterparts derive from petrochemical feedstock.     

Methods for the analysis of PCBs in human food, faeces and serum.

A method was developed to determine trace concentrations of a range of individual PCB congeners in biological samples (serum, food and faeces) using GC-MS, to prepare a mass balance of PCBs in humans. A simple method for the analysis of PCBs in human serum, which excluded an extraction step, was first employed. Results indicated that the recoveries of 13C12 PCB spikes were variable. A soxhlet extraction step was added and was found to be efficient and reproducible. A quality control routine and method validation results are presented. In batch tests of the methods presented it was found that the serum analysis method gave within batch mean 13C12 spike recoveries of 98-120% and standard deviations between 6 and 20%. The food/faeces analysis method gave within-batch mean 13C12 spike recoveries of 88-100%, and within batch standard deviations between 4 and 12%. The batch to batch mean recovery for serum analysis was 100%, with an RSD of 9% for high spikes and 10% for low spikes. For food/faeces analysis the batch to batch average recovery was 110%, with an RSD of 5% for high spikes and 9% for low spikes.     

Real-time indoor and outdoor measurements of black carbon in an occupied house: an examination of sources

Black carbon (BC) was measured every 5 min for two years (May 1998-May 2000) inside and immediately outside a northern Virginia house (suburban Washington, DC) occupied by two nonsmokers. Two aethalometers, which measure BC by optical transmission through a quartz fiber tape, were employed indoors and outdoors. Meteorological parameters were obtained on an hourly basis from nearby Dulles airport. Indoor activities were recorded to identify indoor sources such as combustion activities, which occurred 9% of the time during the first year and 4% of the time during the second year. At times without indoor sources, indoor/outdoor BC ratios averaged 0.53 in the first year and 0.35 in the second year. The main outdoor source of BC was the general regional background, contributing 83-84% of the total during each of the two years. Morning rush hour traffic contributed 8-9% of the total BC. An evening peak in the fall and winter, thought to include contributions from wood burning, was responsible for approximately 8% of the annual average BC concentration. The main indoor sources of BC were cooking and candle burning, contributing 16 and 31%, respectively, of the annual average indoor concentrations in the two years. Relative humidity (RH) affected the outdoor aethalometer in both years. An artifact associated with the tape advance was noted for the aethalometer, but a correction factor was developed that reduced the associated error by a factor of 2.