Methods for collecting time/activity pattern information related to exposure to combustion products

Focus groups, surveys and questionnaires, diaries and observations can be used to gather information about people's exposure to a wide range of combustion products. Information about locations and durations of exposure, and sources of exposure can be obtained with these instruments. The types of instruments used must be fine tuned to meet the design characteristics of the community in which the study will be conducted.     

Preferential bromide and pesticide movement to tile drains under different cropping practices

Subsurface drainage systems are useful tools to study chemical leaching in soils. Our objective was to compare the breakthrough behavior of bromide, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamid] to tile drains under two fall tillage practices (conventional tillage [CT] with a moldboard plow, and reduced tillage [RT] with a chisel plow) in field plots cultivated with corn (Zea mays L.). Leachate volume were greater in RT than in CT, with no statistical differences. Soil analysis showed that bromide migrated deeper in the soil profile than both herbicides, with little tillage effect. All chemicals were detected in drainage water at the same time and followed an event-driven behavior. Tillage had no effect on atrazine and metolachlor found in drainage water, while bromide concentration peaks were higher in RT than in CT in 1999. Concentration peaks were recorded earlier for atrazine and metolachlor than for bromide. Plots of cumulative relative chemical mass (cumulative mass divided by total mass measured in drainage) as a function of cumulative drainage were mostly linear for bromide, while they were S-shaped for both herbicides. Drainage that corresponded to 50% of relative cumulative mass ranged from 40 to 55% for bromide and from 5 to 28% for both herbicides. Rapid chemical movement to tile drains suggested that preferential flow was important in both CT and RT, and that these tillage practices had little influence on this phenomena.     

Soil quality in New Zealand: policy and the science response

Soil depletion and degradation have been increasingly recognized as important environmental issues in many parts of the world. Over the last decade a number of political and legislative measures have been introduced to encourage and enforce sustainable soil management in New Zealand. Application of the new legislation has highlighted gaps in our knowledge of soil quality and a lack of scientific methods to assess and monitor soil quality. This paper describes the legislative measures and outlines the sdentific response to the needs of regulatory agencies responsible for maintaining environmental quality. The research recommended a set of indicators to assess soil quality. Each soil quality attribute has an associated "target range" defining the acceptable value for the attribute. The paper also discusses the communication of results to end-users, including the development of a computerized assessment tool. The legislative measures and scientific response have fostered a closer relationship between the policy and science communities, leading to more well-focused research, but greater collaboration is still required.     

Real-time, high-resolution quantitative measurement of multiple soil gas emissions: selected ion flow tube mass spectrometry

A new technique is presented for the rapid, high-resolution identification and quantification of multiple trace gases above soils, at concentrations down to 0.01 microL L(-1) (10 ppb). The technique, selected ion flow tube mass spectrometry (SIFT-MS), utilizes chemical ionization reagent ions that react with trace gases but not with the major air components (N2, O2, Ar, CO2). This allows the real-time measurement of multiple trace gases without the need for preconcentration, trapping, or chromatographic separation. The technique is demonstrated by monitoring the emission of ammonia and nitric oxide, and the search for volatile organics, above containerized soil samples treated with synthetic cattle urine. In this model system, NH3 emissions peaked after 24 h at 2000 nmol m(-2) s(-1) and integrated to approximately 7% of the urea N applied, while NO emissions peaked about 25 d after urine addition at approximately 140 nmol m(-2) s(-1) and integrated to approximately 10% of the applied urea N. The monitoring of organics along with NH3 and NO was demonstrated in soils treated with synthetic urine, pyridine, and dimethylamine. No emission of volatile nitrogen organics from the urine treatments was observed at levels >0.01% of the applied nitrogen. The SIFT method allows the simultaneous in situ measurement of multiple gas components with a high spatial resolution of < 10 cm and time resolution <20 s. These capabilities allow, for example, identification of emission hotspots, and measurement of localized and rapid variations above agricultural and contaminated soils, as well as integrated emissions over longer periods.     

Soil and litter phosphorus-31 nuclear magnetic resonance spectroscopy: extractants, metals, and phosphorus relaxation times

Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy is an excellent tool with which to study soil organic P, allowing quantitative, comparative analysis of P forms. However, for 31P NMR to be tative, all peaks must be completely visible, and in their correct relative proportions. There must be no line broadening, and adequate delay times must be used to avoid saturation of peaks. The objective of this study was to examine the effects of extractants on delay times and peak saturation. Two samples (a forest litter and a mineral soil sample) and three extractants (0.25 M NaOH, NaOH plus Chelex (Bio-Rad Laboratories, Hercules, CA), and NaOH plus EDTA) were used to determine the differences in the concentration of P and cations solubilized by each extractant, and to measure spin-lattice (T1) relaxation times of P peaks in each extract. For both soil and litter, NaOH-Chelex extracted the lowest concentrations of P. For the litter sample, T1 values were short for all extractants due to the high Fe concentration remaining after extraction. For the soil sample, there were noticeable differences among the extractants. The NaOH-Chelex sample had less Fe and Mn remaining in solution after extraction than the other extractants, and the longest delay times used in the study, 6.4 s, were not long enough for quantitative analysis. Delay times of 1.5 to 2 s for the NaOH and NaOH-EDTA were adequate. Line broadening was highest in the NaOH extracts, which had the highest concentration of Fe. On the basis of these results, recommendations for future analyses of soil and litter samples by solution 31P NMR spectroscopy include: careful selection of an extractant; measurement of paramagnetic ions extracted with P; use of appropriate delay times and the minimum number of scans; and measurement of T1 values whenever possible.     

Ion cycling in hemlock-northern hardwood forests of the southern Lake Superior region: a preliminary study

Upland forests of the southern Lake Superior region are diverse and contain a shifting mosaic of eastern hemlock [Tsuga canadensis (L.) Carr.] and northern hardwood forests dominated by sugar maple (Acer saccharum Marsh.). In this study, we survey the relative effects of management practice (old growth vs. managed), forest cover type (hemlock vs. northern hardwood), and soil great group (Entic Haplorthod vs. Alfic Oxyaquic Fragiorthod) on ion cycling as a precursor to a longer-term, more detailed study. Bulk precipitation, throughfall, and soil leachates at three depths were collected for two growing seasons in eight stands on the Ottawa National Forest in the Upper Peninsula of Michigan. A total of 1210 solutions were analyzed for pH, Na, K, Mg, Ca, Cl, NO3, and SO4. Losses of base cations (Ca, Mg, K) and SO4 from the bottom of the rooting zone generally were greater in old-growth than in managed northern hardwoods on both fragic and nonfragic soils. Leaching losses of base cations and NO3 usually were greater beneath old-growth northern hardwoods than beneath old-growth hemlock on both soil types and for both forest cover types and management practices on fragic than nonfragic soils. Management practice, forest cover type, and soil type all appear to affect ion cycling within these forests. All of the stands featured striking losses of base cations that probably are influenced strongly by NO3 and SO4 in atmospheric deposition.     

Improvements in the two-dimensional nuclear magnetic resonance spectroscopy of humic substances

Understanding pollutant sorption, bioremediation of these pollutants, and their interactions with humic substances requires knowledge of molecular-level processes. New developments with nuclear magnetic resonance (NMR) experiments and labeled compounds have improved the overall understanding of these mechanisms. The advancements made with two-dimensional NMR show great promise, as structural information and hydrogen-carbon bond connectivity can be discerned. This communication presents the application of improved two-dimensional NMR methods, the double quantum filtered (DQF) correlation spectroscopy (COSY) and echo/anti-echo heteronuclear single quantum coherence (HSQC) experiments, for use in structural studies of humic substances. Both experiments were found to produce significant improvements over the conventional COSY and heteronuclear multiple quantum coherence (HMQC) experiments that have been previously employed in similar studies. The more sensitive echo/anti-echo HSQC experiment produced more cross-peaks with higher resolution when compared with the HMQC spectra. The DQF-COSY significantly suppressed the diagonal signals and allowed numerous signals previously hidden in the standard COSY experiment to be observed. These improvements will aid current characterization strategies of humic substances from soils, sediments, and water and their subsequent reactions with pollutants and microorganisms.     

The Lake Erie Agricultural Systems for Environmental Quality project: an introduction

In the last part of the twentieth century, recognition became widespread of the important effect of agricultural runoff on the health of aquatic ecosystems in the Lake Erie basin and elsewhere. Because of the efforts to remediate Lake Erie, the "dead lake" among the Laurentian Great Lakes, a number of research and demonstration projects were undertaken in the Lake Erie basin to evaluate and foster adoption of conservation tillage and other farming techniques that would reduce runoff while maintaining productivity. In addition, intensive water quality studies of long duration were begun on major tributaries to Lake Erie during this time. The Lake Erie Agricultural Systems for Environmental Quality (LEASEQ) project examined governmental programs, changes in agriculture, and changes in water and soil quality during the period 1975-1995, and sought to evaluate the linkages among these factors. The study area is characterized by extensive agricultural land use of soils developed from glacial materials deposited on Paleozoic sedimentary bedrock, mostly limestone. Tile drainage is extensive, particularly in slow-draining clay-rich lacustrine soils in the lower reaches of the watersheds. This paper introduces the study area, its geology, geography, soils, and agricultural history. In addition, we provide an overview of the LEASEQ concept and introduce the 11 other papers in this series, which provide a detailed exposition of the results of our studies.     

Sensitivity and first-step uncertainty analyses for the preferential flow model MACRO

Sensitivity analyses for the preferential flow model MACRO were carried out using one-at-a-time and Monte Carlo sampling approaches. Four different scenarios were generated by simulating leaching to depth of two hypothetical pesticides in a sandy loam and a more structured clay loam soil. Sensitivity of the model was assessed using the predictions for accumulated water percolated at a 1-m depth and accumulated pesticide losses in percolation. Results for simulated percolation were similar for the two soils. Predictions of water volumes percolated were found to be only marginally affected by changes in input parameters and the most influential parameter was the water content defining the boundary between micropores and macropores in this dual-porosity model. In contrast, predictions of pesticide losses were found to be dependent on the scenarios considered and to be significantly affected by variations in input parameters. In most scenarios, predictions for pesticide losses by MACRO were most influenced by parameters related to sorption and degradation. Under specific circumstances, pesticide losses can be largely affected by changes in hydrological properties of the soil. Since parameters were varied within ranges that approximated their uncertainty, a first-step assessment of uncertainty for the predictions of pesticide losses was possible. Large uncertainties in the predictions were reported, although these are likely to have been overestimated by considering a large number of input parameters in the exercise. It appears desirable that a probabilistic framework accounting for uncertainty is integrated into the estimation of pesticide exposure for regulatory purposes.     

Natural uranium and thorium distributions in podzolized soils and native blueberry

Plant uptake of radionuclides is one of many vectors for introduction of contaminants into the human food chain. Thus, it is critical to understand soil-plant relationships that control nuclide bioavailability. Our objectives in this study were to (i) determine the extent of U and Th uptake and cycling by blueberry (Vaccinium pallidum Aiton) in native habitat and (ii) identify the soil properties and processes that contribute most to U and Th bioavailability in this system. We collected composite samples of plant leaves and stems, and samples from surface (AE) horizons and from the upper part of the Bs horizon at two sites. Concentration ratios (CRs) for U and Th were calculated for all plant tissues, using both the AE and Bs horizons as the base. Soil concentrations of U ranged from 16 to 25 microg g(-1), with a mean of 21.1 microg g(-1). Soil concentrations of Th ranged from 14 to 97 microg g(-1), with a mean of 41.8 microg g(-1). Mean U concentrations were 8.65 x 10(-3) microg g(-1) in leaf tissue, and 7.95 x 10(-3) microg g(-1) in stem tissue. Mean Th concentrations were 1.59 x 10(-1) microg g(-1) in leaf tissue, and 9.10 x 10(-2) microg g(-1) in stem tissue. Blueberry plants are cycling both U and Th in this system, with Th cycling occurring to a greater extent than U. In addition, Th was translocated preferentially to plant leaves while U concentrations showed little preferential translocation. Uranium uptake, however, seemed more sensitive than Th uptake to soil properties.