Constructed wetlands for mitigation of atrazine-associated agricultural runoff

Atrazine was amended into constructed wetlands (59-73x14x0.3 m) for the purpose of monitoring transport and fate of the pesticide to obtain information necessary to provide future design parameters for constructed wetlands mitigation of agricultural runoff. Following pesticide amendment, a simulated storm and runoff event equal to three volume additions was imposed on each wetland. Targeted atrazine concentrations were 0 microg/l (unamended control), 73 microg/l, and 147 microg/l. Water, sediment, and plant samples were collected weekly for 35 days from transects longitudinally distributed throughout each wetland and were analyzed for atrazine using gas chromatography. Between 17 and 42% of measured atrazine mass was within the first 30-36 m of wetlands. Atrazine was below detection limits (0.05 microg/kg) in all sediment and plant samples collected throughout the duration of this study. Aqueous half lives ranged from 16 to 48 days. According to these data, conservative buffer travel distances of 100-280 m would be necessary for effective runoff mitigation.     

Chlorpyrifos-methyl dissipation in a small adjacent water body following application to citrus

Chlorpyrifos-methyl use in citrus, vineyards and vegetables is extensive and it has become an essential component of pest control in Southern European regions. The objective of this study was to assess surface water and sediment exposure to chlorpyrifos-methyl (RELDAN 22) under field conditions in a citrus orchard in Sicily (Italy). Pesticide drift loadings were measured in a small surface water body situated 0.5-1.0 m from the edge of the treated field. Measured drift values after the application were between 0.04% and 0.19% of the theoretical applied dose and were highly variable. However, the loadings were lower than those measured by other authors, also lower than predicted by regulatory drift models (95th percentile) typically used for aquatic risk assessment in Europe. Most of the variability occurred due to fluctuating wind speed and direction. In water samples collected in the surface water adjacent to the target field, chlorpyrifos-methyl was detected immediately after application, with concentrations ranging from less than the limit of quantification of the analytical method (0.05 microg/l) to a maximum of 0.08 microg/l. Predicted environmental concentrations in water, using the TOXSWA model, were similar to the measured data when measured drift data from the field experiment were used as inputs.     

Individual and mixture toxicity of three pesticides; atrazine,chlorpyrifos, and chlorothalonil to the marine phytoplankton species Dunaliella tertiolecta

This study analyzed the toxicity of three pesticides (the herbicide atrazine, the insecticide chlorpyrifos and the fungicide chlorothalonil) individually, and in two mixtures (atrazine and chlorpyrifos; atrazine and chlorothalonil) to the marine phytoplankton species Dunaliella tertiolecta (Chlorophyta). A standard 96 h static algal bioassay was used to determine pesticide effects on the population growth rate of D. tertiolecta. Mixture toxicity was assessed using the additive index approach. Atrazine and chlorothalonil concentrations > or = 25 microg/L and 33.3 microg/L, respectively, caused significant decreases in D. tertiolecta population growth rate. At much higher concentrations (> or = 400 microg/L) chlorpyrifos also elicited a significant effect on D. tertiolecta population growth rate, but toxicity would not be expected at typical environmental concentrations. The population growth rate EC50 values determined for D. tertiolecta were 64 microg/L for chlorothalonil, 69 microg/L for atrazine, and 769 microg/L for chlorpyrifos. Atrazine and chlorpyrifos in mixture displayed additive toxicity, whereas atrazine and chlorothalonil in mixture had a synergistic effect. The toxicity of atrazine and chlorothalonil combined was approximately 2 times greater than that of the individual chemicals. Therefore, decreases in phytoplankton populations resulting from pesticide exposure could occur at lower than expected concentrations in aquatic systems where atrazine and chlorothalonil are present in mixture. Detrimental effects on phytoplankton population growth rate could impact nutrient cycling rates and food availability to higher trophic levels. Characterizing the toxicity of chemical mixtures likely to be encountered in the environment may benefit the pesticide registration and regulation process.     

Seasonal exposures to triazine and other pesticides in surface waters in the western Highveld corn-production region in South Africa

The objective of this study was to characterize concentrations of atrazine, terbuthylazine, and other pesticides in amphibian habitats in surface waters of a corn-production area of the western Highveld region (North-West Province) of South Africa. The study was conducted from November 2001 to June 2002, coinciding with the corn-production season. Pesticide residues were measured at regular intervals in surface water from eight ponds, three in a non-corn-growing area (NCGA) and five within the corn-growing area (CGA). Measured atrazine concentrations differed significantly among sites and between samples. In the five CGA sites, the maximum atrazine concentrations measured during the study ranged from 1.2 to 9.3 microg/L. Although no atrazine was recorded as being applied in the catchment of the three NCGA sites, maximum concentrations from 0.39 to 0.84 microg/L were measured during the study, possibly as a result of atmospheric transport. Maximum measured concentrations of terbuthylazine ranged from 1.22 to 2.1 microg/L in the NCGA sites and from 1.04 to 4.1 microg/L in the CGA sites. The source of terbuthylazine in the NCGA sites may have been in use other than in corn. The triazine degradation products, deisopropylatrazine (DIA) and deethylatrazine (DEA) and diaminochlorotriazine (DACT) were also found in water from both the CGA and NCGA sites. Concentrations of DIA were > or = 1 microg/L throughout the season, while DEA concentrations were mostly <0.5 microg/L before planting but increased after planting and application of herbicides to concentrations >2 microg/L in some locations. Concentrations of DACT were highly variable (LOD to 8 microg/L) both before and after planting and application, suggesting that they resulted from historical use of triazines in the area. Other herbicides such as simazine and acetochlor were only detected infrequently and pesticides such as S-metolachlor, cypermethrin, monocrotophos, and terbuphos, known to be used in the CGA, were not detected in any of the samples. Because of dilution by higher than normal rainfall in the study period, these concentrations may not be predictive of those in years of normal rainfall.     

Investigation on downwind short-range transport of pesticides after application in agricultural crops

For the assessment of potential risks from total exposure to both spray drift and volatilised pesticides, field experiments in barley were carried out with insecticide application in May and June 2000. Pesticide concentrations in the air at the edge of the treated plot and at various distances in downwind direction were determined. The concentrations at 10 m distance were 0.29 and 0.58 microg/m(3) (lindane), 0.07 and 0.12 microg/m(3) (parathion) or <0.02 and 0.04 microg/m(3) (pirimicarb) after 1 d. To quantify the exposure of aquatic ecosystems, water containers simulating surface waters were placed in downwind direction of the plot at distances of 10 and 50 m. Lindane as the most volatile and most persistent of the investigated active substances showed the highest entries in surface water with 35 and 153 microg/m(2) after 1 d at a distance of 10 m, attributable to a larger extent to deposition of volatilised compound than to spray drift when drift reducing nozzles were used. Similar results were obtained for parathion, but at a lower level. Mainly due to its photolytic instability in water, pirimicarb decayed in surface water, where a maximum deposition was measured 2 h after application.     

Controls on atrazine leaching through a soil-unsaturated fractured limestone sequence at Brévilles, France

The objective of this study was to identify the main controls on atrazine leaching through luvisols and calcisols overlying fissured limestone using the dual-permeability model MACRO. The model parameterisation was based on a combination of direct measurements (e.g. hydraulic properties, adsorption and degradation), literature data and calibration against bromide leaching experiments in field plots. A Monte Carlo sensitivity analysis was carried out for a typical application pattern, considering two different depths of unsaturated limestone (15 and 30 m). MACRO calibrations to the field experiments demonstrated the occurrence of strong macropore flow in the luvisol, while transport in the calcisol could be described by the advection-dispersion equation. MACRO simulations of tritium and atrazine leaching qualitatively matched tritium concentration profiles measured in the limestone and atrazine concentrations measured in piezometers and in aquifer discharge via a spring. The sensitivity analysis suggested that the thickness of the limestone, as well as the transport properties and processes occurring in the unsaturated rock (e.g. matrix vs. fissure flow) will have little significant long-term effect on atrazine leaching, mainly because degradation is very slow in the limestone. No mineralization of atrazine was detected in one-year incubations and a mean half-life of 10 years was assumed in the simulations. Instead, processes occurring in the soil exerted the main control on predicted atrazine leaching, especially variations in the degradation rate and the strength of sorption and macropore flow. However, fissure flow in unsaturated rock is expected to exert a much more significant control on groundwater contamination for compounds that degrade more readily in the deep vadose zone.     

Clearance of atrazine in soil describing xenobiotic behavior

The primary aim of this study was to evaluate the “clearance concept” as a tool for describing the behavior of xenobiotic movement into and through soils. As an example, degradation of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) with the formation of metabolites 2-chloro-6-isopropylamino-s-triazine (desethylatrazine) and 2-chloro-4-ethylamino-s-triazine (desisopropylatrazine) was investigated. Atrazine was sprayed post-emergently in doses of 0.125 or 0.5 g active ingredient/m² each on four test plots. Soil type was a sandy-loam, on which corn (Zea mays L.) was cultivated. Soil samples were taken as cores of 0.2 m depth 0, 1, 2, 4, 8, 12, 16 and 20 weeks after application of atrazine, and analyzed by HPLC. Soil concentrations of atrazine were highly correlated (r=0.993, p< 0.001) between the two applications of 0.125 g/m² and 0.5 g/m². Up to 50% of the atrazine was measured as metabolites during the whole vegetation period. Clearance of atrazine from soil was calculated as the total load of atrazine divided by the area under the soil atrazine concentration time curve. Soil atrazine clearance was calculated as 5.13 +/? SD 1.10 and 5.17 +/? SD 1.02 liter of soil per day for doses of 0.125 g/m² and 0.5 g/m², respectively (from a “soil unit” of 1 × 1 × 0.2 meter). The clearance concept might be a tool for risk assessment of xenobiotics.     

The effects of elevated metals on benthic community metabolism in a Rocky Mountain stream

The effects of elevated metals (dissolved Zn, Mn and/or Fe) in a Rocky Mountain stream were assessed using measures of primary productivity, community respiration and water-column toxicity. Primary productivity was measured as rates of O2 evolution from natural substrates incubated in situ in closed chambers. Oxygen depletion within these chambers, when incubated in the dark, provided estimates of periphyton community respiration. Sediment community respiration on fine-grained sediments, collected and composited along each stream study reach, was measured on-site by incubating these sediments in closed chambers and measuring O2 depletion. Toxicity was measured as percent mortality of Ceriodaphnia dubia during 48 h acute tests. Gross (GPP) and net primary productivity (NPP) decreased significantly with increasing metal concentrations, from 10.88 +/- 1.46 g O2 m(-2) day(-1) to 0.83 +/- 0.20 g O2 m(-2) day(-1) and 9.85 +/- 1.43 g O2 m(-2) day(-1) to 0.81 +/- 0.20 g O2 m(-2) day(-1), respectively for the reference and most impacted site. Community respiration (CR) declined from 0.65 +/- 0.08 g O2 m(-2) day(-1) to 0.02 +/- 0.01 g O2 m(-2) day(-1) with increasing metal concentrations. Sediment community respiration (SCR) decreased from 0.26 +/- 0.02 g O2 m(-2) day(-1) to 0.01 +/- 0.01 g O2 m(-2) day(-1) at these same sites. Ceriodaphnia dubia mortality increased from 0% at the reference site to 95 +/- 5% at the most impacted sites. Net daily metabolism, quantum yield and assimilation ratio all decreased with increasing metal concentrations, suggesting that both autotrophic and heterotrophic components of the periphyton community were impaired. Overall, functional measures were able to discern sites receiving greater metal impacts from less-impacted sites, with combinations of dissolved metals explaining between 25 and 92% of the variance in the regression models. Using these regression models we were able to calculate lethal and inhibition concentrations of dissolved Zn in the Eagle River. The lethal concentration (LC50) of Zn for Ceriodaphnia dubia is 123 mg liter(-1). The concentrations of Zn which inhibited respiration (IC50) were 177 mg liter(-1) for CR and 199 mg liter(-1) for SCR. These results indicate functional measures may be as sensitive to metal concentrations as acute toxicity tests.     

Phosphorus in waters from sewage sludge amended lysimeters

In surface waters, phosphorus (P) concentrations exceeding 0.05 mg liter(-1) may cause eutrophic conditions. This study was undertaken to measure total P concentrations in runoff and tile drainage waters from land receiving either inorganic fertilizer or anaerobically digested sewage sludge. Total P was measured in runoff and tile drainage waters during 2 years of sample collections from instrumented, large-scale lysimeters planted to corn (Zea mays L.). During the 3 years prior to monitoring P concentrations, six of the lysimeter plots had been amended with anaerobically digested sewage sludge which supplied 5033 kg P per ha. Additional sludge applications supplied 1058 and 1989 kg P per ha during the first and second years of monitoring operations, respectively. Another six lysimeters were annually treated with fertilizer which included P applications amounting to 112 kg ha(-1). For years 1 and 2, respectively, annual losses from lysimeters treated with sewage sludge were 4.27 and 0.35 kg P per ha in runoff and 0.91 from 0.91 and 0.51 kg Per P per ha in drainage waters. Parallel annual losses of P from lysimeters treated with superphosphate were 2.15 and 0.17 kg ha(-1) in runoff and 0.53 and 0.35 kg ha(-1) in tile drainage waters. Sludge applications did not significantly change absolute soil contents of organic P, but did decrease the per cent of total P present in organic forms. Sludge and soil, respectively, contained 21 and 36% of their total P contents in organic forms. In sludge and soil about 85 and 64% of their respective total inorganic P contents were associated with the Al and Fe fractions. Sludge applications significantly increased soil contents of P in the saloid (water-soluble plus P extracted with 1 N NH(4)Cl), Al, Fe and reductant soluble P fractions, but contents of Ca-bound P were not changed. Total P contents of the soil below a depth of 30 cm were not affected by sludge incorporated to a depth of about 15 cm by plowing.     

Seasonal and spatial patterns of metals at a restored copper mine site II. Copper in riparian soils and Bromus carinatus shoots

Soil and plants were sampled throughout winter and spring near a perennial stream traversing a restored mine site in a winter-rainy climate. Within 1m of an acidic reach of the stream, soil had pH 3-5 and 50-100 microg/g "bioavailable" copper (extractable with 0.01 M CaCl2). Soil 2-3 m from the stream had pH 5-8 and lower (less than 3 microg/g) bioavailable copper. "Oxide-bound" copper (extractable with 2N HCl) was 50-100 microg/g at most locations. Copper concentrations in the shoots of field-collected Bromus carinatus declined from 20 microg/g in winter to 2 microg/g in spring at all sampling sites. A similar temporal pattern was found in plants grown under controlled conditions. Thus B. carinatus has a developmental program for control of shoot copper concentration, causing a seasonally-varying pattern of copper phytoaccumulation over a large range of copper availability in the soil.     

Assessment of insecticide contamination in runoff and stream water of small agricultural streams in the main soybean area of Argentina

The first- and second-order streams, Brown and Horqueta, respectively, which are located in the main area of soybean production in Argentina were examined for insecticide contamination caused by runoff from nearby soybean fields. The insecticides most widely used in Argentina (chlorpyrifos, cypermethrin and endosulfan) were detected in sediments, suspended particles and water. Highest concentrations in suspended particles were 318 microg/kg for endosulfan in the stream Horqueta, while 226 microg/kg chlorpyrifos and 13.2 microg/kg cypermethrin were measured in the stream Brown. In the Horqueta stream 150 and 53 microg/kg chlorpyrifos and cypermethrin were detected in runoff sediments, respectively. Whereas cypermethrin concentrations in the suspended particles were relatively low, levels in the floodwater of Brown reached 0.7 microg/l. The highest chlorpyrifos concentration in floodwater was 0.45 microg/l in Brown. However, endosulfan was not detected in the water phase. In runoff water the highest concentrations measured were 0.3 microg/l for chlorpyrifos in Horqueta and 0.49 microg/l for cypermethrin in the Brown stream. On five sampling dates during the pesticide application period in Brown stream (2002/2003) the concentration of chlorpyrifos and cypermethrin in runoff and/or floodwater exceeded the water quality criteria for freshwater mentioned in this study. In three cases this insecticide concentration was measured in stream water, indicating an acute risk to aquatic life. The acute toxicity-exposure-ratio (TER) for chlorpyrifos and cypermethrin also shows an acute risk for aquatic invertebrates in the Brown stream. In the Horqueta chlorpyrifos concentrations in the runoff exceeded the safety levels three times during the application period (2001/2002), potentially endangering the aquatic fauna. Effects on aquatic macroinvertebrates after insecticide contamination were reported in earlier studies in Horqueta stream.     

Determination of commonly used polar herbicides in agricultural drainage waters in Australia by HPLC

The present study describes the application of different extraction techniques for the preconcentration of ten commonly found acidic and non-acidic polar herbicides (2,4-D, atrazine, bensulfuron-methyl, clomazone, dicamba, diuron, MCPA, metolachlor, simazine and triclopyr) in the aqueous environment. Liquid-liquid extraction (LLE) with dichloromethane, solid-phase extraction (SPE) using Oasis HLB cartridges or SBD-XC Empore disks were compared for extraction efficiency of these herbicides in different matrices, especially water samples from contaminated agricultural drainage water containing high concentrations of particulate matter. Herbicides were separated and quantified by high performance liquid chromatography (HPLC) with an ultraviolet detector. SPE using SDB-XC Empore disks was applied to determine target herbicides in the Murrumbidgee Irrigation Area (NSW, Australia) during a two-week survey from October 2005 to November 2005. The daily aqueous concentrations of herbicides from 24-h composite samples detected at two sites increased after run-off from a storm event and were in the range of: 0.1-17.8 microg l(-1), < 0.1-0.9 microg l(-1) and 0.2-17.8 microg l(-1) at site 1; < 0.1-3.5 microg l(-1), < 0.1-0.2 microg l(-1) and < 0.2-3.2 microg l(-1) at site 2 for simazine, atrazine and diuron, respectively.     

Long-term dynamics of the atrazine mineralization potential in surface and subsurface soil in an agricultural field as a response to atrazine applications

The dynamics of the atrazine mineralization potential in agricultural soil was studied in two soil layers (topsoil and at 35-45 cm depth) in a 3 years field trial to examine the long term response of atrazine mineralizing soil populations to atrazine application and intermittent periods without atrazine and the effect of manure treatment on those processes. In topsoil samples, ¹⁴C-atrazine mineralization lag times decreased after atrazine application and increased with increasing time after atrazine application, suggesting that atrazine application resulted into the proliferation of atrazine mineralizing microbial populations which decayed when atrazine application stopped. Decay rates appeared however much slower than growth rates. Atrazine application also resulted into the increase of the atrazine mineralization potential in deeper layers which was explained by the growth on leached atrazine as measured in soil leachates recovered from that depth. However, no decay was observed during intermittent periods without atrazine application in the deeper soil layer. atzA and trzN gene quantification confirmed partly the growth and decay of the atrazine degrading populations in the soil and suggested that especially trzN bearing populations are the dominant atrazine degrading populations in both topsoil and deeper soil. Manure treatment only improved the atrazine mineralization rate in deeper soil layers. Our results point to the importance of the atrazine application history on a field and suggests that the long term survival of atrazine degrading populations after atrazine application enables them to rapidly proliferate once atrazine is again applied.     

Uncertainty in Nonpoint Source Pollution Models and Associated Risks

The usefulness of water quality simulation models for environmental management is explored with a focus on prediction uncertainty. The specific objective is to demonstrate how the usability of a flow and transport model (here: MACRO) can be enhanced by developing and analyzing its output probability distributions based on input variability. This infiltration-based model was designed to investigate preferential flow effects on pollutant transport. A statistical sensitivity analysis is used to identify the most uncertain input parameters based on model outputs. Probability distribution functions of input variables were determined based on field-measured data obtained under alternative tillage treatments. Uncertainty of model outputs is investigated using a Latin hypercube sampling scheme (LHS) with restricted pairing for model input sampling. Probability density functions (pdfs) are constructed for water flow rate, atrazine leaching rate, total accumulated leaching, and atrazine concentration in percolation water. Results indicate that consideration of input parameter uncertainty produces a 20% higher mean flow rate along with two to three times larger atrazine leaching rate, accumulated leachate, and concentration than that obtained using mean input parameters. Uncertainty in predicted flow rate is small but that in solute transport is an order of magnitude larger than that of corresponding input parameters. Macropore flow is observed to contribute to the variability of atrazine transport results. Overall, the analysis provides a quantification of prediction uncertainty that is found to enhance a user's ability to assess risk levels associated with model predictions.     

Assessment of the effects of herbicide spray drift on a range of plant species of conservation interest

With increasing use of herbicides there has been growing concern that spray drift from treated land will affect vegetation on adjacent nature reserves and other areas of high conservation interest. A preliminary attempt was made to assess this risk by placing a range of native plant species at different distances downwind from standardised drift events and assessing lethal effects and sublethal damage. Five herbicides were tested: asulam, 'Finesse' (chlorsulfuron + metsulfuron-methyl), glyphosate, MCPA and mecoprop. Applications were made at the appropriate time of years for each herbicide (autumn, spring and summer), and at both low and high wind speeds. The maximum safe distance at which no lethal effects were found was 6 m from the sprayer, but for most herbicides the distance was 2 m or less. Generally, damage symptoms were found at greater distances than lethal effects, but in most cases there was rapid recovery by the end of the growing season. These observations are consistent with drift-deposition models, in which the fallout of herbicide droplets has been measured. It is suggested that buffer zones surrounding nature reserves should be in the order of 5-10 m for ground sprayers to minimise the risk of herbicide impacts on these habitats.     

Pollution-induced community tolerance (PICT) and seasonal variations in the sensitivity of phytoplankton to atrazine in nanocosms.

Algae communities exposed to a herbicide like atrazine (PS II inhibitor) are expected to be selected and to be more tolerant to the herbicide than unexposed communities (pollution-induced community tolerance, PICT). The PICT may be an ecotoxicological tool for detecting this selective action of chronic pollution, and this method has been applied to several toxicants in experimental systems and in field studies. But the detection of PICT with PS II inhibitors has sometimes been variable. This work was done to study the long-term effects of exposure to atrazine (10 microg/l) and the PICT responses of phytoplankton communities in repeated outdoor nanocosms. Phytoplankton communities were sampled in Lake Geneva at different periods of the year and the effects of atrazine were analysed by studying community structure, biomass and primary production, and by measuring tolerance to atrazine in a short-term physiological test based on 14C incorporation. We find that PICT is a sensitive method for measuring effects. Even atrazine concentrations causing little restructuring induced tolerance in most of our experiments. But the short- and long-term responses of phytoplankton to atrazine varied between experiments, probably due to the initial compositions of the communities and environmental factors associated with seasonal parameters. The selection and detection steps of PICT to atrazine thus vary greatly with environmental conditions and the physiological adaptations of algae to the herbicide. To monitor risk assessment in aquatic systems, PICT studies applied to algae, must be investigated in the light of seasonal contaminations and seasonal events and successions.     

Impact of a pulse application of permethrin on the macroinvertebrate community of a headwater stream

This study evaluated the impact of concentrated pulse (16 microg litre(-1)) of the insecticide permethrin (emulsifiable concentrate) on the macroinvertebrate community of a northern Ontario headwater stream. Post-treatment drift increased by a factor of 2400 within minutes of the arrival of the insecticide. There was a significant (P<0.05) reduction in the abundance of invertebrates in most families as far as 260 m below the point of injection in both kick and artificial substrate samples. Greatest impact was observed in the mayflies, Baetis flavistriga. Heptagenia flavescens, and Epeorus sp., the stonefly, Leuctra tenuis, and the caddisfly, Dolophilodes distinctus. Diptera were not significantly reduced. The number of species occurring 100 m from the point of injection was reduced by 47%, but only by 17% at 260 m. There was no change in the per cent composition of functional feeding groups at any point after treatment. Recovery of most invertebrates was complete within 6 weeks of treatment.     

Pesticide concentrations in agricultural storm drainage inlets of a small Swiss catchment

Agricultural pesticides transported to surface waters pose a major risk for aquatic ecosystems. Modelling studies indicate that the inlets of agricultural storm drainage systems can considerably increase the connectivity of surface runoff and pesticides to surface waters. These model results have however not yet been validated with field measurements. In this study, we measured discharge and concentrations of 51 pesticides in four out of 158 storm drainage inlets of a small Swiss agricultural catchment (2.8 km²) and in the receiving stream. For this, we performed an event-triggered sampling during 19 rain events and collected plot-specific pesticide application data. Our results show that agricultural storm drainage inlets strongly influence surface runoff and pesticide transport in the study catchment. The concentrations of single pesticides in inlets amounted up to 62 µg/L. During some rain events, transport through single inlets caused more than 10% of the stream load of certain pesticides. An extrapolation to the entire catchment suggests that during selected events on average 30 to 70% of the load in the stream was transported through inlets. Pesticide applications on fields with surface runoff or spray drift potential to inlets led to increased concentrations in the corresponding inlets. Overall, this study corroborates the relevance of such inlets for pesticide transport by establishing a connectivity between fields and surface waters, and by their potential to deliver substantial pesticide loads to surface waters.

     

Concentration and size distribution of ultrafine particles near a major highway

Motor vehicle emissions usually constitute the most significant source of ultrafine particles (diameter <0.1 microm) in an urban environment, yet little is known about the concentration and size distribution of ultrafine particles in the vicinity of major highways. In the present study, particle number concentration and size distribution in the size range from 6 to 220 nm were measured by a condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS), respectively. Measurements were taken 30, 60, 90, 150, and 300 m downwind, and 300 m upwind, from Interstate 405 at the Los Angeles National Cemetery. At each sampling location, concentrations of CO, black carbon (BC), and particle mass were also measured by a Dasibi CO monitor, an aethalometer, and a DataRam, respectively. The range of average concentration of CO, BC, total particle number, and mass concentration at 30 m was 1.7-2.2 ppm, 3.4-10.0 microg/m3, 1.3-2.0 x 10(5)/cm3, and 30.2-64.6 microg/m3, respectively. For the conditions of these measurements, relative concentrations of CO, BC, and particle number tracked each other well as distance from the freeway increased. Particle number concentration (6-220 nm) decreased exponentially with downwind distance from the freeway. Data showed that both atmospheric dispersion and coagulation contributed to the rapid decrease in particle number concentration and change in particle size distribution with increasing distance from the freeway. Average traffic flow during the sampling periods was 13,900 vehicles/hr. Ninety-three percent of vehicles were gasoline-powered cars or light trucks. The measured number concentration tracked traffic flow well. Thirty meters downwind from the freeway, three distinct ultrafine modes were observed with geometric mean diameters of 13, 27, and 65 nm. The smallest mode, with a peak concentration of 1.6 x 10(5)/cm3, disappeared at distances greater than 90 m from the freeway. Ultrafine particle number concentration measured 300 m downwind from the freeway was indistinguishable from upwind background concentration. These data may be used to estimate exposure to ultrafine particles in the vicinity of major highways.     

Uptake and accumulation of mercury from dental amalgam in the common goldfish,Carassius auratus

In this study, the bioavailability and accumulation of mercury from external environmental exposure to mixed, cured, milled, sieved and proportioned dental amalgam was examined in the common goldfish, Carassius auratus. Fish were exposed to dental amalgam (particle size range from < 0.10 to 3.15 mm) in order to represent the particle size and distribution of that found within the typical dental office wastewater discharge stream. Experimental amalgam water loadings were 0 g/l, 0.5 g/l and 1 g/l in glass aquaria at 15 degrees C for 28 days. Fish tissues were sampled at 5 min and 28 days of exposure, and the liver, brain, muscle and whole body analyzed for total mercury using cold vapor atomic fluorescence spectroscopy. Mercury was found in several tissues examined and generally increased with exposure to higher amounts of dental amalgam. The highest levels were found in the whole body (17.68 +/- 5.73 microg/g) followed by the liver (0.80 +/- 0.16 microg/g) and muscle (0.47 +/- 0.16 microg/g). The lowest concentrations were seen in the brain (0.28 +/- 0.19 microg/g). Compared to controls, concentrations in the whole body, muscle and liver in fish exposed for 28 days to the highest concentration of amalgam were 200-, 233-, and 40-fold higher, respectively. This study shows that mercury from an environmental exposure to representative samples of dental amalgam typically found within the dental wastewater discharge stream is bioavailable to fish and may accumulate in internal tissues.