Incubation time effects on imazaquin desorption as determined by nonequilibrium thin-soil disc flow

Because organic sorption in soil may never reach equilibrium, a thin-disc flow nonequilibrium method may be helpful in understanding herbicide-soil interactions. This research was conducted to (i) determine the influence of incubation time on imazaquin [2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-3-quinolinecarboxylic acid] desorption from soil, (ii) examine the influence of solution flow velocities on desorption, and (iii) elucidate the most appropriate kinetic model to describe imazaquin leaching. Soil at 7.5% moisture w/w was treated with imazaquin and incubated for 24, 72, and 168 h. Treated soil was sealed in an in-line filter apparatus and rinsed with 5.0 mM CaCl2 at 0.33, 0.67, or 1.0 mL min(-1). Effluent was collected as 1.0-mL fractions for a total of 50 mL. Flow was stopped for 24 h. When flow resumed, fractions were collected for an additional 15 mL. After the initial desorption, 79% of the imazaquin incubated for 24 h was leached. Increasing incubation time beyond 24 h reduced imazaquin leaching. After both desorption events, 13% of the initially applied imazaquin remained in the soil incubated for 168 h, compared with 7% with soil incubated for 24 h. Elovich and Freundlich kinetics accounted for 98% of the variance observed in the imazaquin desorption curves. First-order and diffusion kinetics accounted for 91% of the variance. Incubating soil for 72 h before desorption reduced the rate of imazaquin desorption by approximately 12%, compared with the 24-h incubation treatment. Imazaquin desorption was not affected by wash solution flow rate. These data suggest that the kinetics of desorption in prolonged desorption events are limited by transport phenomena (i.e., particle and film diffusion).     

Phosphorus transfer in surface runoff from intensive pasture systems at various scales: a review

Phosphorus transfer in runoff from intensive pasture systems has been extensively researched at a range of scales. However, integration of data from the range of scales has been limited. This paper presents a conceptual model of P transfer that incorporates landscape effects and reviews the research relating to P transfer at a range of scales in light of this model. The contribution of inorganic P sources to P transfer is relatively well understood, but the contribution of organic P to P transfer is still relatively poorly defined. Phosphorus transfer has been studied at laboratory, profile, plot, field, and watershed scales. The majority of research investigating the processes of P transfer (as distinct from merely quantifying P transfer) has been undertaken at the plot scale. However, there is a growing need to integrate data gathered at a range of scales so that more effective strategies to reduce P transfer can be identified. This has been hindered by the lack of a clear conceptual framework to describe differences in the processes of P transfer at the various scales. The interaction of hydrological (transport) factors with P source factors, and their relationship to scale, require further examination. Runoff-generating areas are highly variable, both temporally and spatially. Improvement in the understanding and identification of these areas will contribute to increased effectiveness of strategies aimed at reducing P transfers in runoff. A thorough consideration of scale effects using the conceptual model of P transfer outlined in this paper will facilitate the development of improved strategies for reducing P losses in runoff.     

Lead reduction and redistribution in the forest floor in New Hampshire northern hardwoods

Because of the affinity of organic matter for lead, atmospheric loadings of this pollutant have been strongly retained in the forest floor. With the regulation of Pb emissions, loadings have decreased. We measured changes in Pb in forest floor horizons at a variety of northern hardwood sites in New Hampshire from the late 1970s to the 1990s. In all seven of the sites in which horizons were distinguished within the forest floor, Pb was found to be declining in the upper (Oie) horizon, but not in the underlying Oa and A horizons. At the Hubbard Brook Experimental Forest (HBEF), this loss from the Oie resulted in a 36% loss of Pb from the forest floor as a whole between 1976 and 1997 (p < 0.001). In contrast, in six stands in the Bartlett Experimental Forest (BEF), losses of Pb averaging >50% from the Oi and Oe horizons (p = 0.01) between 1979 and 1994 were compensated by gains in the Oa and A horizons. Similarly, at seven additional stands in the White Mountain National Forest, changes in the forest floor as a whole from 1980 to 1995 were not statistically significant (redistribution within the forest floor was not evaluated at these sites). Lead concentrations were highest in the Oe or Oie in the 1970s, but were highest in the Oa horizon in the 1990s. There was no significant pattern of Pb loss or retention as a function of stand age across all the sites.     

Runoff phosphorus losses as related to phosphorus source, application method, and application rate on a Piedmont soil

Land application of animal manures and fertilizers has resulted in an increased potential for excessive P losses in runoff to nutrient-sensitive surface waters. The purpose of this research was to measure P losses in runoff from a bare Piedmont soil in the southeastern United States receiving broiler litter or inorganic P fertilizer either incorporated or surface-applied at varying P application rates (inorganic P, 0-110 kg P ha(-1); broiler litter, 0-82 kg P ha(-1)). Rainfall simulation was applied at a rate of 76 mm h(-1). Runoff samples were collected at 5-min intervals for 30 min and analyzed for reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP). Incorporation of both P sources resulted in P losses not significantly different than the unfertilized control at all application rates. Incorporation of broiler litter decreased flow-weighted concentration of RP in runoff by 97% and mass loss of TP in runoff by 88% compared with surface application. Surface application of broiler litter resulted in runoff containing between 2.3 and 21.8 mg RP L(-1) for application rates of 8 to 82 kg P ha(-1), respectively. Mass loss of TP in runoff from surface-applied broiler litter ranged from 1.3 to 8.5 kg P ha(-1) over the same application rates. Flow-weighted concentrations of RP and mass losses of TP in runoff were not related to application rate when inorganic P fertilizer was applied to the soil surface. Results for this study can be used by P loss assessment tools to fine-tune P source, application rate, and application method site factors, and to estimate extreme-case P loss from cropland receiving broiler litter and inorganic P fertilizers.     

Evaluation of catalyzed and electrically heated filters for removal of particulate emissions from diesel-A- and JP-8-fueled engines

In-service diesel engines are a significant source of particulate matter (PM) emissions, and they have been subjected to increasingly strict emissions standards. Consequently, the wide-scale use of some type of particulate filter is expected. This study evaluated the effect of an Engelhard catalyzed soot filter (CSF) and a Rypos electrically heated soot filter on the emissions from in-service diesel engines in terms of PM mass, black carbon concentration, particle-bound polycyclic aromatic hydrocarbon concentration, and size distribution. Both filters capture PM. The CSF relies on the engine's exhaust to reach the catalyst regeneration temperature and oxidize soot, whereas the electrically heated filter contains a heating element to oxidize soot. The filters were installed on several military diesel engines. Particle concentrations and compositions were measured before and after installation of the filter and again after several months of operation. Generally, the CSF removed at least 90% of total PM, and the removal efficiency improved or remained constant after several months of operation. In contrast, the electrical filters removed 44-69% of PM mass. In addition to evaluating the soot filters, the sampling team also compared the results of several real-time particle measurement instruments to traditional filter measurements of total mass.     

Contrasting effects of manure and compost on soil pH, heavy metal availability and growth of Chenopodium album L. in a soil contaminated by pyritic mine waste

Chenopodium album L. was found to be one of the initial plant species colonising a heavy metal-contaminated site, polluted by pyritic (sulphide-rich) waste from the Aznalcóllar mine spill (South-western Spain). This indicates its importance in the re-vegetation of this soil. In a pot experiment, C. album was sown in soil collected from the contaminated site, either non-amended or amended with cow manure or compost produced from olive leaves and olive mill wastewater, in order to study the effect on heavy metal bioavailability and soil pH. In non-amended and compost-amended soils, soil acidification, probably resulting from oxidation and hydrolysis of sulphide, led to increases in the concentrations of soluble sulphate and plant-available Cu, Zn and Mn in the soil (extractable with 0.1 M CaCl(2)). Under these conditions, shoot growth of C. album was negligible and shoot concentrations of Zn (2,420-5,585 microg g(-1)) and Mn (5,513-8,994 microg g(-1)) were phytotoxic. Manure application greatly increased shoot growth and reduced the shoot concentrations of Cu, Zn, and Mn, and their plant-available concentrations in the soil. These effects appeared to be related to an increase of soil pH, due to an inhibition of sulphide oxidation/hydrolysis, relative to the non-amended soil. For metal sulphides-contaminated soil, liable to acidification, manure application appears to be able to enhance the initial stages of re-vegetation, by species such as C. album.     

The uptake of uranium by Eleocharis dulcis (Chinese water chestnut) in the Ranger Uranium Mine constructed wetland filter

Eleocharis dulcis has proliferated in a constructed wetland used to treat uranium mine runoff water, where it rapidly accumulates significant quantities of uranium (U) in its roots and relatively little in its stems. We investigated the mechanism of U uptake and accumulation by E. dulcis using field-sampling techniques and microcosm test work. Results from the microcosm trials and outcomes from statistical tests of field sampled macrophyte, water and sediment indicate that the primary source of U for E. dulcis is the water column. Basipetal translocation of U to the plant's roots was indicated by significant correlations between the U content of stems, taproots and rhizomes and XPS detection of U inside root segments. U sequestering from sediment interstitial water by Fe hydroxides on root surfaces was also evident. No basipetal translocation was evident following the 28-day duration of the microcosm experiments, indicating that it is a longer-term process.     

Development and validation of a method for analysis of "dioxin-like" PCBs in environmental samples from the steel industry

A method, previously used for determination of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), has been modified for quantitative analysis of "dioxin-like" polychlorobiphenyls (PCBs) in environmental samples from the steel industry. The existing sample clean-up procedure, involving liquid chromatography on multi-layered silica and Florisil columns, has been extended to include a third chromatography stage on a basic alumina stationary phase. The additional clean-up stage is required for PCB analysis in order to eliminate interferences from relatively large concentrations of saturated cyclic and aliphatic hydrocarbons. Samples were analysed for WHO-12 congeners using high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) and standard solutions of the method US EPA 1668A. Replicate analysis of method blanks revealed background contamination for PCBs 118, 105 and 77, which are generally abundant in ambient air. These contaminants were taken into account using a subtraction method. The entire procedure was validated by replicate analysis (N = 3) of a certified reference sediment. The RSD for each WHO-12 congener was below 15%, 13C12-labelled PCB internal standard recoveries were in the range 70-95%. A waste dust sample collected in the electrostatic precipitator of a UK sinter plant was analysed for determination of PCDD/Fs and WHO-12 PCBs and exhibited a PCDD/F I-TEQ of 148.5 +/- 21.2 ngkg(-1) and a WHO-TEQ of 7.2 +/- 1.5 ngkg(-1). WHO-12 congeners contributed only 4.6% to the overall TEQ and PCB 126 was the major congener contributing to the WHO-TEQ (96%). The contribution to the overall TEQ of the waste dust sample was mainly attributed to PCDF followed by PCDD, which accounted for 86.6% and 8.7% to the overall TEQ, respectively.     

Correlations in the chemical composition of rural background atmospheric aerosol in the UK determined in real time using time-of-flight mass spectrometry

An aerosol time-of-flight mass spectrometer (ATOFMS) was used to determine, in real time, the size and chemical composition of individual particles in the atmosphere at the remote inland site of Eskdalemuir, Scotland. A total of 51,980 particles, in the size range 0.3-7.4 microm, were detected between the 25th and 30th June 2001. Rapid changes in the number density, size and chemical composition of the atmospheric aerosol were observed. These changes are attributed to two distinct types of air mass; a polluted air mass that had passed over the British mainland before reaching Eskdalemuir, interposed between two cleaner air masses that had arrived directly from the sea. Such changes in the background aerosol could clearly be very important to studies of urban aerosols and attempts at source apportionment. The results of an objective method of data analysis are presented. Correlations were sought between the occurrence of: lithium, potassium, rubidium, caesium, beryllium, strontium, barium, ammonium, amines, nitrate, nitrite, boron, mercury, sulfate, phosphate, fluorine, chlorine, bromine, iodine and carbon (both elemental and organic hydrocarbon) in both fine (d < 2.5 microm) and coarse (d > 2.5 microm) particle fractions. Several previously unreported correlations were observed, for instance between the elements lithium, beryllium and boron. The results suggest that about 2 in 3 of all fine particles (by number rather than by mass), and 1 in 2 of all coarse particles containing carbon, consisted of elemental carbon rather than organic hydrocarbon (although a bias in the sensitivity of the ATOFMS could have affected these numbers). The ratio of the number of coarse particles containing nitrate anions to the number of particles containing chloride anions exceeded unity when the air mass had travelled over the British mainland. The analysis also illustrates that an air mass of marine origin that had travelled slowly over agricultural land can accumulate amines and ammonium.     

The ecological relevance of current approaches for environmental protection from exposure to ionising radiation

This paper discusses the current approaches to environmental protection from ionising radiation from an ecological perspective, highlighting the need to understand fully what we are trying to protect. Ecologically relevant endpoints for environmental protection are discussed along with the need to integrate protection from ionising radiation with the approaches adopted for non-radioactive contaminants. A possible integrated assessment approach is outlined.