Hydrolysis of chlorpyrifos in natural waters of the Chesapeake Bay

Chlorpyrifos is the most widely used insecticide in the Chesapeake Bay region. Recent studies show that this organophospate chemical is consistently present in the air, rain and surface waters of the Chesapeake Bay region, suggesting a long environmental half-life. Hydrolytic degradation of chlorpyrifos is likely a dominant removal process, but existing hydrolysis data do not reflect conditions in the Chesapeake Bay. In this project, hydrolysis rates of chlorpyrifos were measured in sterilized, ambient water from the mouth of four Chesapeake Bay tributaries ranging in salinity from 0 to 17 ppt. The measured hydrolysis half-lives varied from 24 d in the Patuxent River to 126 d in the Susquehanna River. These results indicate that pH alone cannot be used as a single parameter to predict hydrolysis under field conditions. The influence of copper concentration, and other water constituents, need to be further evaluated as they may emerge as independent predictors to assess the fate of pesticides in natural systems.     

Atmospheric deposition of organic carbon to Chesapeake Bay

The organic carbon content of wet and bulk deposition was measured from February through to December 1981 at four stations surrounding Chesapeake Bay. Organic carbon is removed from the atmosphere in association with both wet and dry deposition. Regional yearly wet and dry depositional rates were approximately equal, with a total yearly deposition rate of 11.3 g C m⁻² y⁻¹. Atmospheric deposition provides an important flux of organic material to Chesapeake Bay and must be considered if biogeochemical cycles are to be fully understood.     

Bulk atmospheric deposition of hydrocarbons to lower Chesapeake Bay

Anthropogenic and biogenic hydrocarbons (HC) were continuously deposited from the atmosphere at stations in SE Virginia. The bulk deposition rate for total unresolved complex mixture (UCM) and n-alkane HC was constant at all stations during the sampling period (> 1 year). The deposition rates at the three non-urban stations was similar and averaged 69, 27 and 18 μg m⁻² d⁻¹ for total, UCM and n-alkane HC, respectively. The urban station had a higher deposition rate for total (203 μg m⁻² d⁻¹) and UCM (90 μg m⁻² d⁻¹) HC than the non-urban stations, but a similar deposition rate for n-alkanes (22 μg m⁻²d⁻¹). These results indicate a regionally similar deposition rate for biogenic (n-alkanes) and anthropogenic (UCM) HC, with a major localized input of anthropogenic HC at the urban station. Long range atmospheric transport followed by dry deposition appear to be the major processes responsible for these similar deposition rates over this geographical area.     

Improved daily precipitation nitrate and ammonium concentration models for the Chesapeake Bay Watershed

Daily precipitation nitrate and ammonium concentration models were developed for the Chesapeake Bay Watershed (USA) using a linear least-squares regression approach and precipitation chemistry data from 29 National Atmospheric Deposition Program/National Trends Network (NADP/NTN) sites. Only weekly samples that comprised a single precipitation event were used in model development. The most significant variables in both ammonium and nitrate models included: precipitation volume, the number of days since the last event, a measure of seasonality, latitude, and the proportion of land within 8km covered by forest or devoted to industry and transportation. Additional variables included in the nitrate model were the proportion of land within 0.8km covered by water and/or forest. Local and regional ammonia and nitrogen oxide emissions were not as well correlated as land cover. Modeled concentrations compared very well with event chemistry data collected at six NADP/AirMoN sites within the Chesapeake Bay Watershed. Wet deposition estimates were also consistent with observed deposition at selected sites. Accurately describing the spatial distribution of precipitation volume throughout the watershed is important in providing critical estimates of wet-fall deposition of ammonium and nitrate.     

Sorption and bioreduction of hexavalent uranium at a military facility by the Chesapeake Bay

Directly adjacent to the Chesapeake Bay lies the Aberdeen Proving Ground, a U.S. Army facility where testing of armor-piercing ammunitions has resulted in the deposition of >70,000 kg of depleted uranium (DU) to local soils and sediments. Results of previous environmental monitoring suggested limited mobilization in the impact area and no transport of DU into the nation's largest estuary. To determine if physical and biological reactions constitute mechanisms involved in limiting contaminant transport, the sorption and biotransformation behavior of the radionuclide was studied using geochemical modeling and laboratory microcosms (500 ppb U(VI) initially). An immediate decline in dissolved U(VI) concentrations was observed under both sterile and non-sterile conditions due to rapid association of U(VI) with natural organic matter in the sediment. Reduction of U(VI) to U(IV) occurred only in non-sterile microcosms. In the non-sterile samples, intrinsic bioreduction of uranium involved bacteria of the order Clostridiales and was only moderately enhanced by the addition of acetate (41% vs. 56% in 121 days). Overall, this study demonstrates that the migration of depleted uranium from the APG site into the Chesapeake Bay may be limited by a combination of processes that include rapid sorption of U(VI) species to natural organic matter, followed by slow, intrinsic bioreduction to U(IV).     

Mathematical Model for Photocatalytic Destruction of Organic Contaminants in Air

Abstract

Photocatalytic oxidation (PCO) was investigated in a bench-scale reactor for the abatement of two airborne organic contaminants: toluene and ethanol. A mathematical model that includes the impacts of light intensity, initial contaminant concentration, catalyst thickness, and relative humidity (RH) on the degradation of organic contaminants in a photocatalytic reactor was developed to describe this process. The commercially available catalyst Degussa-PtTiO₂ was selected to compare with the MTU-PtTiO₂-350 catalyst, which was synthesized by the sol-gel process, platinized, and calcined at 350 °C. For toluene removal using the MTU-PtTiO₂-350 catalyst, the degradation rate increased with increases in light intensity from 0.2 to 2.2 mW/cm² and in catalyst thickness from 0.00037 to 0.00361 cm. However, further increases in light intensity and catalyst thickness had only slight effect on the toluene degradation rate. Increasing the initial concentration from 6.29 to 127.9 μg/L and the RH from 10 to 85% resulted in decreases in the toluene degradation rate. For ethanol removal using the MTU-PtTiO₂- 350 catalyst, the degradation rate increased more rapidly with an increase in RH from 17 to 56%; the RH had little effect on the ethanol degradation rate while it further increased from 56% to 82%. We discuss applicability of the model to estimate the influence of process variables and to evaluate photocatalyst performance.     

Polychlorinated biphenyls and particulate organic/elemental carbon in the atmosphere of Chesapeake Bay,USA

Polychlorinated biphenyls (PCBs) and particulate organic/elemental carbon (OC/EC) differ as to sources, but are both elevated in major urban areas leading to loadings of proximate terrestrial and aquatic systems. Because of the dramatic difference in speciation, sources, and sinks of these compunds, gas+particulate phase PCBs and particulate OC/EC were measured in urban Baltimore, MD and over Chesapeake Bay at 4 and 12 h frequencies in July 1997. Gas phase ∑PCBs averaged 1180 pg m⁻³ for Baltimore and 550 pg m⁻³ for northern Chesapeake Bay. PCB homolog distributions in the gas phase differed between the land and over-water sites whereby the trichlorobiphenyls were higher in Baltimore compared to Chesapeake Bay. Autocorrelation analysis yielded a diurnal cycle for gas phase PCBs at Baltimore with the lowest concentrations observed during the day. Particulate organic and elemental carbon constituted 12.4% (17.4% organic matter) and 2.8% of total suspended particles (TSP) in Baltimore, and 15.0% (21.0% organic matter) and 5.3% over the Chesapeake Bay, respectively. Variability in PCB concentrations was not related to the variability in OC/EC concentrations. OC/EC ratios suggest that particulate organic carbon was mostly primary aerosol. Emissions of both classes of compounds into the Baltimore atmosphere and vicinity are major sources to the Bay.     

Impact of Polycyclic Aromatic Hydrocarbon Emissions from Medical Waste Incinerators on the Urban Atmosphere

Abstract

In this study, polycyclic aromatic hydrocarbon (PAH) emissions from two batch-type medical waste incinerators (MWIs), one with a mechanical grate and the other with a fixed grate, both operated by a medical center, were assessed. Both MWIs shared the same air-pollution control devices (APCDs), with an electrostatic precipitator and a wet scrubber installed in series. Results show that when APCDs were used, total PAHs and total benzo- [a]pyrene equivalent (total BaP_eq) emission concentrations of both MWIs were reduced from 2220 to 1870 µg/m³ and 50 to 12.4 µg/m³, respectively. We used the Industrial Source Complex Short Term model (ISCST) to estimate the ground-level concentrations of the residential area and the traffic intersection located at the down-wind side of the two MWIs. For the traffic intersection, we found both total PAHs and total BaP_eq transported from MWIs to both studied areas were not significant. For the residential area, similar results were found when APCDs were used in MWIs. When APCDs were not included, we found that total PAHs transported from MWIs accounted for <12%, but total BaP_eq accounted for >90%, of the on-site measured concentrations. These results suggest that the use of proper APCDs during incineration would significantly reduce the carcinogenic potencies associated with PAH emissions from MWIs to the residential area.     

Processes driving the short-term variability of polycyclic aromatic hydrocarbons in the Baltimore and northern Chesapeake Bay atmosphere,USA

Polycyclic aromatic hydrocarbons (PAHs) were measured in the Baltimore and adjacent Chesapeake Bay in July 1997. Time series of 4- and 12-h samples were taken at two sites 15 km apart in order to evaluate the influence of a number of processes on the short-term variability of PAH in the Baltimore and northern Chesapeake Bay atmospheres. PAH concentrations were 2–3-fold higher in the Baltimore atmosphere than in the adjacent Chesapeake Bay atmosphere. For example, gas-phase phenanthrene and pyrene concentrations were 12.5 and 2.14 ng m⁻³ in the Baltimore site and 5.57 and 0.548 ng m⁻³ in the Chesapeake Bay, respectively. The influence of wind direction, wind speed and temperature was evaluated by multiple linear regressions which indicated that atmospheric gas-phase PAH concentrations over the Chesapeake Bay were significantly higher when the air mass was from the urban/industrial Baltimore area. Furthermore, the increase of gas-phase low-MW PAH concentrations with temperature and wind speed suggests that volatilization from the bay is an important source of pollutants to the atmosphere, at least when air masses are not influenced by the Baltimore urban and industrial area. Indeed, while on the long-term, the Chesapeake Bay is a receptor of atmospherically deposited PAHs, on the short-term and during appropriate meteorological conditions, the bay acts as a source of pollutants to the atmosphere. Aerosol-phase PAH concentrations and temporal trends showed a strong dependence on aerosol soot content due to the high affinity of PAHs to the graphitic structure of soot. These results confirm the important influence of urban areas as a source of pollution to adjacent aquatic environments and as a driving factor of the short-term variability, either directly by transport of urban-generated pollutants or by volatilization of previously deposited pollutants. Conversely, the complex diurnal trends of gas-phase PAHs at the Baltimore site suggests that degradation processes dominate the diurnal trends of PAHs in urban atmospheres. This conclusion is supported by estimated rate constants for PAH reaction with OH radicals which show good agreement with reported values within a factor of two.     

Relation of Benzene Soluble Organic Matter to Suspended Participate Matter in the Atmosphere

This paper presents information concerning the response to the availability of control program grants under Sect. 4 of the Clean Air Act, P.L. 88-206. Statistics concerning awards are presented together with a discussion of the nature of the projects supported and the impact of this support on air pollution control efforts throughout the country.     

Determination of Volatile Organic Compounds in the Atmosphere Using Two Complementary Analysis Techniques

ABSTRACT

During a preliminary field campaign of volatile organic compound (VOC) measurements carried out in an urban area, two complementary analysis techniques were applied to establish the technical and scientific bases for a strategy to monitor and control VOCs and photochemical oxidants in the Autonomous Community of the Basque Country. Integrated sampling was conducted using Tenax sorbent tubes and laboratory analysis by gas chromatography, and grab sampling and in situ analysis also were conducted using a portable gas chromatograph. With the first technique, monocyclic aromatic hydrocarbons appeared as the compounds with the higher mean concentrations. The second technique allowed the systematic analysis of eight chlorinated and aromatic hydrocarbons. Results of comparing both techniques, as well as the additional information obtained with the second technique, are included.     

Numerical evaluation of the PCBs transport over the Northern Hemisphere

The numerical evaluation of selected PCB congener (28, 118, 153, 180) transport over the Northern Hemisphere is carried out for 1996 using MSCE-POP model. This model is a multicompartment three-dimensional one and includes various environmental media such as the atmosphere, soil, vegetation, seawater, and sea ice. The spatial resolution is 2.5 degrees x2.5 degrees for all media except marine one (1.25 degrees x1.25 degrees ). The main model output information is deposition fluxes, spatial distribution of concentrations in environmental media, pathways and source-receptor relationships. Calculation results are analysed for the whole hemisphere and the Arctic region. In particular, this gives an opportunity to estimate the contributions of individual emission source groups to the Arctic pollution. The reliability of the model assessment is analysed by comparison between calculated and observed data.     

Gas-Particle Distribution Factors for Organic and Other Pollutants in the Los Angeles Atmosphere

The distribution of organic pollutants between the gas and particu-late phases was measured for 6 days Including one with the highest ozone level observed in Pasadena In 1973 (7/25). Gas phase pollutants were monitored continuously while particulates were sampled over a one hour interval by filtration. The filters were extracted using a polar and a non-polar solvent; particulate organic carbon was determined using a carbon analyzer, and chemical analysis carried out by fractionation, gas chromatography, infrared, and CHON analysis.

The organic carbon fraction (OCF) was always large, up to 43% of the total particulates (TP). Most of the organics were oxygenated compounds of photochemical origin. There was a linear relation between O₃, OCF, and the infrared carbonyl band intensities of the extracts. Hourly variations of OCF and TP are discussed with respect to the gas phase pollutants and conversion processes.

Although secondary pollutant concentrations were found in the order: organics > nitrates > sulfates, nitrates were more efficient than organics in visibility degradation, based on a statistical evaluation of the data. The secondary aerosol contribution varied with O₃, accounting for up to 95% of TP when the O₃ peaked. The unusual nitrate peak observed for 7/25 is discussed with the atmospheric chemistry of other nitrogen compounds.

We define an organic carbon distribution factor: f_c = particulate organic carbon (POC, μg/m³C)/[POC + gas phase reactive hydrocarbons (μg/m³C)]. The gas-particle distribution factors for organics (f_c), nitrates (f_N) and sulfates (f_s) are in inverse order of their aerosol concentrations: f_c < f_N < f_s . The measured f_c are low: average 2–3%, highest value 6% for 7/25, and correspond to a conversion rate ≤2% hour^?1. Ambient f_c are much lower than f_c measured for certain specific hydrocarbon precursors.     

Differences in the bioaccumulation of arsenic by oysters from Southeast coastal US and Chesapeake Bay: environmental versus genetic control

The potential sources of relatively great concentrations of arsenic (As) in oysters from the Southeastern United States coast was examined in a study conducted from August 1998 through October 1999. A transplant experiment was conducted to determine whether genetic or environmental differences accounted for the observed difference between Southeastern oysters, and oysters elsewhere on the east coast. Oysters originating in South Carolina (a region where As in oysters is usually greater) and Maryland (a region where arsenic is oysters is less) were reciprocally transplanted to determine whether site of growth or site of origin would determine the accumulation of As. To examine the potential role of various potential sources of As exposure on the concentrations of As in oysters, samples of native oysters, water, pore water and suspended particles were collected and analyzed for As monthly, while the sediments were examined four times during the year. Concentrations of As in transplanted oysters matched the concentrations of As in oysters native to the area in which they were grown, rather than that of oysters from their site of origin. Oysters from South Carolina had average concentrations of As approximately 3.2 times that of oysters from Maryland. This enrichment was similar to enrichments of water (3.4 times), sediment (2.5 times), suspended particles (1.7 times), and pore water (3.1 times) from South Carolina compared to Maryland. This supports the hypothesis that the cause of the apparent As enrichments in the Southeastern oysters is environmental, but leaves the question of the primary source for arsenic incorporation by oysters open.     

Total Volatile Organic Compounds in the Urban Environment of Delhi

ABSTRACT

Total volatile organic compounds (TVOCs) in the urban ambient environment of Delhi were monitored from November 1994 to June 1995 at 13 sites using an inexpensive and a manual-labor-intensive sample collection procedure in want of sophisticated equipment. The results of the study show appreciable levels of TVOCs in the ambient environment of Delhi. The amount of TVOCs in the ambient environment was found to vary between 3 and 42 ppmv and exhibited wide temporal and seasonal variations. On a diurnal cycle, TVOC levels mostly peaked at 9:00 a.m., which coincided with the peak traffic hour. TVOC buildup in the urban atmosphere has serious implications for air quality through the formation of highly toxic oxidants. The results of this preliminary study make out a strong case for a regular monitoring of TVOCs in the urban environment of Delhi.     

Role of manganese oxides in the exposure of mute swans (Cygnus olor) to Pb and other elements in the Chesapeake Bay, USA

The aims of this study are to estimate exposure of waterfowl to elements in contaminated sediments in the Chesapeake Bay and to consider the potential role of Mn in influencing bioavailability and exposure. Metal concentrations were measured in livers and digesta taken from mute swans living on the Aberdeen Proving Ground, whose sediment had elevated concentrations of Cu, S, Se, Zn, As, Co, Cr, Hg and Pb. Concentrations of only the first four of these elements were elevated in swan digesta. None of the concentrations detected in the digesta or livers of the swans was considered toxic, although the concentrations of Cu and Se were high compared to concentrations of these elements reported in other waterfowl. Lead was found to be scavenged by Mn and Fe oxides from the water and deposited on the surface of vegetation at a reference site. Under some environmental chemical conditions, this is an important route of exposure to Pb in waterfowl, not previously recognized.     

Influence of boundary conditions on CMAQ simulations over the Iberian Peninsula

The influence of chemical boundary conditions (BC) on the response of the Community Multiscale Air Quality (CMAQ) model over the Iberian Peninsula was investigated in this study. Three strategies to supply boundary conditions in the context of the Integrated Assessment Modelling System for the Iberian Peninsula (SIMCA) were tested. Alternative methods consist in providing BC from (1) fixed, time-independent, concentration profiles, (2) concentrations predicted in a CMAQ mother domain (48 km, 1 h resolution) and (3) concentration values from the GEOS-Chem chemical-transport global model (2 × 2.5°, 3 h resolution). High resolution (3 km) simulated concentrations of the main pollutants (NO₂, NO, SO₂, O₃, PM₁₀ and PM_2.5) were compared through a comprehensive statistical analysis including observational data from 165 monitoring stations all over the Iberian Peninsula. It was found that model sensitivity to BC for nitrogen and sulphur oxides was limited, being restricted to the vicinity of model boundaries. However, significant domain-wide differences were found when modelling ozone and PM depending on the BC provided to run the tests. Although model performance was affected by spatial and seasonal factors, the results indicate that model-derived, dynamic BC improved CMAQ predictions when compared to those based on static concentrations prescribed in the boundaries. Aggregated statistics suggest that the GEOS-Chem produced the best results for O₃ and PM_2.5 while NO₂ and PM₁₀ were slightly better predicted under the CMAQ nesting approach. Besides the statistical evaluation some other relevant issues in the context of Integrated Assessment Modelling (IAM) are discussed to gain a better insight into the suitability of the methods analyzed and limitations of downscaling methods. Despite being useful to get a better understanding of the role of BC in SIMCA, this study contributed to highlight model deficiencies and therefore to point out future research needs to improve IAM activities in the Iberian Peninsula.     

Application of WRF-Chem to simulate air quality over Northern Vietnam

Environmental Science and Pollution Research - The WRF-Chem (Weather Research and Forecasting with Chemistry) model is implemented and validated against ground-based observations for meteorological...