Degradation of N,N'-dibutylurea (DBU) in soils treated with only DBU and DBU-fortified benlate fungicides

N,N'-dibutylurea (DBU) is a breakdown product of benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazole carbamate], the active ingredient in Benlate fungicides, and has been proposed to cause crop damage after the use of Benlate 50 DF fungicide (DuPont, Wilmington, DE). Our research focused on DBU persistence after application into soil. We assessed DBU persistence on direct application of DBU (carbonyl-(14)C) at two concentrations (0.08 and 0.8 microg DBU kg(-1)) to seven soils and two potting mixes in soil microcosms incubated at various combinations of soil water potential (-0.03 or -0.1 MPa) and temperature (23, 33, 44 degrees C). For two soils at a subset of treatment variables we assessed DBU persistence in the presence of Benlate DF and SP fungicide formulations. Parent compounds, metabolites, and (14)CO(2) were tracked using chromatographic analysis with radioassay and UV detection, liquid scintillation counting, and post-extraction oxidation of the soil. DBU degradation was primarily microbial and for most soil-treatment combinations, half-lives were less than 2 wk. DBU degradation was retarded at the lower soil water potential and enhanced at 33 degrees C. In the presence of the formulation, DBU degradation was slower for one soil type. The longest half-life observed in any case was less than 7 wk; therefore, long-term persistence of DBU applied to soils through a Benlate application is very unlikely.     

Effects of flooding and drought on water quality in Gulf Coastal Plain streams in Georgia

Since 1994, water-quality constituents have been measured monthly in three adjacent Coastal Plain watersheds in southwestern Georgia. During 1994, rainfall was 650 mm above annual average and the highest flows on record were observed. From November 1998 through November 2000, 19 months had below average rainfall. Lowest flows on record were observed during the summer of 2000. The watersheds are human-dominated with row-crop agriculture and managed forestlands being the major land uses. However, one watershed (Chickasawhatchee Creek) had 10 to 13% less agriculture and greater wetland area, especially along the stream. Suspended particles, dissolved organic carbon, NH4-N, and soluble reactive phosphorus concentrations were greater during wet and flood periods compared with dry and drought periods for each stream. Regional hydrologic conditions had little effect on NO3-N or dissolved inorganic carbon. Chickasawhatchee Creek had significantly lower suspended sediment and NO3-N concentrations and greater organic and inorganic carbon concentrations, reflecting greater wetland area and stronger connection to a regional aquifer system. Even though substantial human land use occurred within all watersheds, water quality was generally good and can be attributed to low stream drainage density and relatively intact floodplain forests. Low drainage density minimizes surface run-off into streams. Floodplain forests reduce nonpoint-source pollutants through biological and physical absorption. In addition to preserving water quality, floodplain forests provide important ecological functions through the export of nutrients and organic carbon to streams. Extreme low flows may be disruptive to aquatic life due to both the lack of water and to the scarcity of biologically important materials originating from floodplain forests.     

Concentration changes for 5 PCDD/F congeners after administration in beef cattle

Ten cattle were treated with daily doses of five PCDD/F congeners, over a 4 week period. Four control animals were not treated. They were subsequently slaughtered as three groups, at 5, 18 and 31 weeks after the first dose. All congeners showed an increase in concentration within animal tissues when sampled at 5 weeks post-dosing. Concentrations had reduced after 18 weeks and there was a further small reduction after 31 weeks. Halflives for each congener were calculated at 13-21 weeks (93-148 days). Concentrations of congeners were different in the various tissues analysed. At 5 weeks after dosing commenced, concentrations in sub-cutaneous fat and in perirenal fat were close to 40 ng/kg (a predicted level based on 50% absorption of the dosed compounds). Concentrations on a fat basis in muscle tissue and liver were, however, about 5 and 10 times higher, respectively. The concentrations found in muscle tissue and liver samples taken at 18 and 31 weeks were approximately twice that found in fat deposits, thus the differences were still apparent, but at a reduced level. It is possible that the distribution phase was incomplete and that PCDD/Fs remained predominantly in association with circulating blood lipids rather than in equilibrium with depot fat. It follows that if livestock were recently exposed to PCDD/Fs (for example, through the consumption of contaminated feed), the analysis of depot fats would not necessarily provide a reliable indicator of the concentrations of PCDD/Fs in edible tissues.     

Seasonal aerosol sulfate trends for selected regions of the United States

Site and regional trends in seasonally averaged particle SO4(2-) concentrations were examined for a large portion of the United States using data collected by the CASTNet air monitoring network. Trends were analyzed for overlapping periods of 1988-1999 and 1992-1999. The largest absolute SO4(2-) decreases--approximately -0.4 microg/m3/yr--between 1988 and 1999 occurred in summer for sites in the Ohio River Valley and areas to the east. Generally, the largest SO4(2-) reductions were found for summer, but larger relative reductions often occurred for spring and autumn. Sulfate changes during 1992-1999 were quite different from those found for 1988-1999 and were not entirely consistent with changes in SO2 emissions. In some locations, the 1992-1999 period saw smaller declines in SO4(2-), while in other places seasonal SO4(2-) actually increased. Increases were mostly confined to summer and autumn across the southern and southwestern states. Multivariate analysis of ambient sulfur levels, by region, versus SO2 emissions reveals that annual emissions are associated with more than 80% of the variance in seasonal sulfur (SO2 and SO4(2-)) in more than three-quarters of the cases examined. The weakest associations were found for the southeastern United States.     

Satellite and Ground Based Monitoring of Aerosol Plumes

Plumes of atmospheric aerosol have been studied using a rangeof satellite and ground-based techniques. The Sea-viewing WideField-of-view Sensor (SeaWiFS) has been used to observe plumesof sulphate aerosol and Saharan dust around the coast of theUnited Kingdom. Aerosol Optical Thickness (AOT) was retrievedfrom SeaWiFS for two events; a plume of Saharan dusttransported over the United Kingdom from Western Africa and aperiod of elevated sulphate experienced over the Easternregion of the UK. Patterns of AOT are discussed and related tothe synoptic and mesoscale weather conditions. Furtherobservation of the sulphate aerosol event was undertaken usingthe Advanced Very High Resolution Radiometer instrument(AVHRR). Atmospheric back trajectories and weather conditionswere studied in order to identify the meteorologicalconditions which led to this event. Co-located ground-basedmeasurements of PM₁₀ and PM_2.5 were obtained for 4sites within the UK and PM_2.5/10 ratios were calculatedin order to identify any unusually high or low ratios(indicating the dominant size fraction within the plume)during either of these events. Calculated percentiles ofPM_2.5/10 ratios during the 2 events examined show thatthese events were notable within the record, but were in noway unique or unusual in the context of a 3 yr monitoringrecord. Visibility measurements for both episodes have beenexamined and show that visibility degradation occurred duringboth the sulphate aerosol and Saharan dust episodes.     

Uptake and release of cesium-137 by five plant species as influenced by soil amendments in field experiments

Phytoextraction field experiments were conducted on soil contaminated with 0.39 to 8.7 Bq/g of 137Cs to determine the capacity of five plant species to accumulate 137Cs and the effects of three soil treatments on uptake. The plants tested were redroot pigweed (Amaranthus retroflexus L. var. aureus); a mixture of redroot pigweed and spreading pigweed (A. graecizans L.); purple amaranth (A. cruteus L.) x Powell's amaranth (A. powellii S. Watson), referred to here as the amaranth hybrid; Indian mustard [Brassica juncea (L.) Czern.]; and cabbage (Brassica oleracea L. var. capitata). For control plants, the concentration ratios (CR) of 137Cs were greatest for redroot pigweed and the amaranth hybrid, with average CR values of 1.0 +/- 0.24 and 0.95 +/- 0.14, respectively. The lowest value was for Indian mustard at 0.36 +/- 0.10. The soil treatments included (i) application of NH4NO3 solution to the soil after plants had matured, (ii) addition of composted manure to increase organic matter content of the soil, (iii) combination of the manure and ammonium solution treatments, and (iv) controls. The ammonium solution gave little overall increase in accumulation of 137Cs. The use of composted manure also had little influence, but the combination of the composted manure with application of ammonium solutions had a distinctly negative effect on plant uptake of 137Cs. On average the fraction of 137Cs taken up from the soil was reduced by 57.4 +/- 1.2% compared with controls. This was the result of release of competing ions, primarily Ca, from the manure and was observed across all five plant species tested. The application of ammonium solution took place in the last two weeks before harvest. The reduction of plant 137Cs content, by addition of the ammonium solution, as it interacted with the manure, indicates that substantial quantities 137Cs can be released from the shoots of plants as a result of sudden changes in soil solution chemistry.     

Changes in wetlands on nonfederal rural land of the conterminous United States from 1982 to 1987

Recent wetland area trends were estimated from the National Resources Inventory (NRI) for nonfederal rural lands for the period 1982–1987. NRI-based estimates of wetland area for states comprising the conterminous United States were highly correlated with estimates made by the US Fish and Wildlife Service and with estimates of coastal salt marsh wetlands made by the National Oceanic and Atmospheric Administration. Net wetland area declined by 1.1% (≈363,200 ha) during the five-year study period. Conversion to open water, primarily caused by natural flooding in western inland basins, was responsible for altering extensive wetland areas (≈171,400 ha). Of the human-induced wetland conversions, urban and built-up land was responsible for 48% of the wetland loss, while agricultural development was indicated in 37% of the converted wetland area. A decrease in rural land, and increases in both population, and urban and built-up land were associated with wetland loss among states. Potential reasons for wetland loss were different in 20 coastal states than in 28 inland states. Proportionately, wetland loss due to development was three times greater in coastal states than inland states, while agriculturally induced wetland losses were similar in both groups. The proportionate declines of forested vs nonforested wetlands were not significantly different among states.     

Sources and factors controlling the disposal of biodegradable municipal solid waste in urban and rural areas of Cyprus

An inventory of sources of biodegradable municipal soil waste (BMSW) was constructed for urban and rural areas in the EU accession region of Cyprus. Composition analysis was performed on source-separated BMSW collected from households in the rural Ergates Community and an urban area within the Agglanjia Municipality. The data were statistically scrutinized to identify the main factors influencing the quantities of BMSW disposed by urban and rural communities in Cyprus. The results were extrapolated to predict the quantities and types of BMSW disposed by the entire communities. Significantly more BMSW was disposed in the urban area compared to the rural community due to lower diversion rates for green waste and the disposal of food waste from commercial sources. The quantity of food waste collected from households was influenced by socio-economic (household size, income, percentage of children) and behavioural (feeding of food waste to domestic animals, consuming processed 'ready' food) factors, whereas garden size, the type of vegetation, the reuse of trimmings and home composting were the main factors controlling the disposal of green waste.