Latitudinal and seasonal capacity of the surface oceans as a reservoir of polychlorinated biphenyls

The oceans play an important role as a global reservoir and ultimate sink of persistent organic pollutants (POPs) such as polychlorinated biphenyls congeners (PCBs). However, the physical and biogeochemical variables that affect the oceanic capacity to retain PCBs show an important spatial and temporal variability which have not been studied in detail, so far. The objective of this paper is to assess the seasonal and spatial variability of the ocean's maximum capacity to act as a reservoir of atmospherically transported and deposited PCBs. A level I fugacity model is used which incorporates the environmental variables of temperature, phytoplankton biomass, and mixed layer depth, as determined from remote sensing and from climatological datasets. It is shown that temperature, phytoplankton biomass and mixed layer depth influence the potential PCB reservoir of the oceans, being phytoplankton biomass specially important in the oceanic productive regions. The ocean's maximum capacities to hold PCBs are estimated. They are compared to a budget of PCBs in the surface oceans derived using a level III model that assumes steady state and which incorporates water column settling fluxes as a loss process. Results suggest that settling fluxes will keep the surface oceanic reservoir of PCBs well below its maximum capacity, especially for the more hydrophobic compounds. The strong seasonal and latitudinal variability of the surface ocean's storage capacity needs further research, because it plays an important role in the global biogeochemical cycles controlling the ultimate sink of PCBs. Because this modeling exercise incorporates variations in downward fluxes driven by phytoplankton and the extent of the water column mixing, it predicts more complex latitudinal variations in PCBs concentrations than those previously suggested.     

Effects of cadmium, copper, lead and zinc on growth, reproduction and survival of the earthworm Eisenia fetida (Savigny): Assessing the environmental impact of point-source metal contamination in terrestrial ecosystems

The earthworm Eisenia fetida (Annelida: Oligochaeta) was exposed to a geometric series of concentrations of cadmium, copper, lead and zinc in artificial soil using the OECD recommended protocol. Mortality, growth and cocoon production were measured over 56 days to determine LC50 and EC50 values. No observed effect concentrations (NOECs) were also estimated. Furthermore, the percentage of viable cocoons and number of juveniles emerging per cocoon was recorded. Cocoon production was more sensitive than mortality for all the metals, particularly cadmium and copper for which NOEC reproduction values were an order of magnitude lower than those for NOEC mortality. However, there was no significant effect of metals on the viability of cocoons. The weights of earthworms declined in all treatments (including the controls) during the experiment. This was probably due to the lack of suitable food in the OECD standard soil medium used. It was concluded that future experiments should include animal manure in the test medium. The LC50, EC50 and NOEC values determined in this study were compared with concentrations of metals in soils in the vicinity of a smelting works at Avonmouth, southwest England. The 14-day LC50 for zinc in Eisenia fetida was exceeded in soils covering an area of 75 km2 around the works, compared to 4.2 km2 for copper and 4.7 km2 for lead. Soil values for cadmium did not exceed the LC50 value anywhere in the region. Similar estimates of relative effects on reproduction confirmed that zinc is most likely to be responsible for the absence of earthworms from sites close to the Avonmouth works. However, the OECD standard test overestimated the potential effects of metals on populations, since earthworms can be found as close as 1 km from the smelting works. The discrepancy between test and field observations was probably due to the greater availability of the metals in the artificial soil.     

Measured and predicted volatilisation fluxes of PCBs from contaminated sludge-amended soils

A laboratory experiment was carried out to measure volatilisation fluxes of polychlorinated biphenyls (PCBs) from sewage sludge-amended soils. The most commonly practised methods of applying sludge to agricultural land in the UK, namely, surface application, ploughing in to soil and subsurface injection, were simulated inside glass experimental chambers using an anaerobically digested sludge and a sandy loam soil. Humidified air was blown over the surface of the soil/sludge in the chambers for a period of 32 days, in order to sample a sufficient air volume to detect the volatilising PCBs. The resulting PCB volatilisation fluxes from the different sludge application methods were quantified and compared. Volatilisation fluxes of individual congeners were generally highest for the surface sludge (1-cm depth) application and slightly lower for the plough layer (5-cm depth) application. Fluxes from the subsurface layer of sludge (5-cm depth) were only quantified for the lightest congeners near to the end of the experimental run-time. Results from a multiple regression analysis showed that volatilisation fluxes of PCBs from the surface application are highly dependent on both the sludge concentration and the log of the octanol-air partition coefficient (K(OA)). A well-known soil volatilisation model, developed by Jury et al., was adapted and used to predict fluxes for the different sludge application methods during the experiment. The model predicted volatilisation fluxes that were reasonably comparable to measured fluxes for some congeners, but for others predicted fluxes that were more than an order of magnitude lower than measured fluxes. The model predicted similar loss kinetics to those observed in the experiment. Possible reasons for the dissimilarity between measured and predicted fluxes include inaccuracies in model input parameters and the fact that the models were not developed for predicting fluxes from sludge-amended soils.     

Fate of 1,2,3,4,6,7,8-heptachlorodibenzofuran and pentachlorophenol during laboratory-scale anaerobic mesophilic sewage sludge digestion

The possibility of the formation of PCDDs and dechlorination of PCDFs during the anaerobic digestion of sewage sludge in laboratory scale digesters was investigated. Digesters were spiked with 1,2,3,4,6,7,8-HpCDF-13C(6) (240 ng/g organic matter (OM)) and pentachlorophenol (PeCP)-13C(6) (24 microg/g OM) and the output sludge monitored for 60 days. No dechlorination or formation of the labelled or native PCDD/Fs was observed. The detectable 1,2,3,4,6,7,8-HpCDF-13C(6) dechlorination yield was 0.0008-1% depending on homologue group and the detectable formation of OCDD yield was 0.00042% PeCP-13C(6). Preferential respiration of other, more bioavailable, substrates is suggested as the most plausible explanation for the lack of dechlorination. Formation of PCDDs from PeCP has been observed in aerobic environments but this study provides further evidence that it is not a precursor for formation during anaerobic digestion.     

Biochemical composition and digestive enzyme activity in larvae and postlarvae ofPenaeus japonicus during herbivorous and carnivorous feeding

The growth, survival, digestive enzyme activity and biochemical composition ofPenaeus japonicus (Bate) larvae and postlarvae were measured under three feeding regimes. Larvae were reared through the protozoeal stages usingChaetoceros gracilis. From the first mysis stage, three feeding regimes were used; (A)C. gracilis plusArtemia sp. nauplii, (B)Artemia sp. nauplii alone or (C)C. gracilis alone. No significant difference was found in growth, survival, protein content or lipid content of postlarvae from the treatments receiving the single-feed type, despite the low protein (7%) and highly unsaturated fatty acid content of the alga. Growth of larvae receiving the mixed diet was significantly higher than in the other treatments. Trypsin activity was more strongly influenced than amylase activity by dietary treatment, and differences in the ratio of these enzymes between treatments suggest independent control of their secretion. Trypsin activity recorded in larvae feeding onC. gracilis was up to six time higher than in larvae feeding onArtemia sp. nauplii, apparently in response to the low protein content of the alga. Larvae receiving the mixed diet exhibited an intermediate level of trypsin activity; it is suggested that the ingestion of algae is necessary for optimal assimilation of the zooplankton component of the diet.     

Dynamic model for the assessment of radiological exposure to marine biota

A generic approach has been developed to simulate dynamically the uptake and turnover of radionuclides by marine biota. The approach incorporates a three-compartment biokinetic model based on first order linear kinetics, with interchange rates between the organism and its surrounding environment. Model rate constants are deduced as a function of known parameters: biological half-lives of elimination, concentration factors and a sample point of the retention curve, allowing for the representation of multi-component release. The new methodology has been tested and validated in respect of non-dynamic assessment models developed for regulatory purposes. The approach has also been successfully tested against research dynamic models developed to represent the uptake of technetium and radioiodine by lobsters and winkles. Assessments conducted on two realistic test scenarios demonstrated the importance of simulating time-dependency for ecosystems in which environmental levels of radionuclides are not in equilibrium.     

Airborne gamma survey of the historic Sleisbeck mine area in the Northern Territory, Australia, and its use for site rehabilitation planning

An airborne gamma-survey provided information about the extent of radioactive contamination around the historic Sleisbeck mine. Quickbird satellite data were acquired to relate airborne measurements to land cover features. Enhanced equivalent uranium (eU) levels were found to be confined to the mine and low grade waste rock dumps. The average terrestrial background radiation dose rate estimated from the airborne gamma survey data was 0.10-0.14 microGy h(-1) while the area around the mine exhibited a maximum of approximately 2.3 microGy h(-1), but measurements on the ground indicate that this maximum is exceeded in some localized areas. Rehabilitation of the site is likely to result in a threefold reduction in radiation doses to people accessing the area.