Trichloroacetic acid in the vegetation of polluted and remote areas of both hemispheres—Part I. Its formation,uptake and geographical distribution

Trichloroacetic acid (TCA; CCl₃COOH) is a phytotoxic chemical. Although TCA salts and derivatives were once deployed as herbicides against perennial grasses and weeds, their use has since been banned because of their indiscriminate herbicidal effects on woody plant species. However, TCA can also be formed in the atmosphere. For instance, high-volatile C₂-chlorohydrocarbons tetrachloroethene (TECE, C₂Cl₄) and 1,1,1-trichloroethane (TCE, CCl₃CH₃) can react to TCA and other substances under oxidative conditions here. Owing to further industrialisation of Southeast Asia, South Africa and South America, a rise can be expected in the use of TECE as solvents in the metal and textile industries of these regions in the southern hemisphere (SH). The increasing emissions of this substance—together with the rise in the atmospheric oxidation potential caused by urban activities, slash and burn agriculture and forest fires in the SH—will result in the increased input/formation of TCA in the vegetation located on the lee side of these emission sources. By means of biomonitoring studies, inputs/formation of TCA related to the climatic conditions were detected at various locations in South America, Africa, and Europe.     

Airborne trichloroacetic acid and its deposition in the catchment area of the Caspian Sea

The main sources of pollution discharge into the Caspian Sea are metal and oil processing plants in the catchment areas of the Ural and Volga rivers, as well as the coastal and offshore oil industry in the countries bordering the sea. The high evaporation from the surface of this largest inland sea introduces highly volatile C₂-chlorohydrocarbons into the atmosphere. Subsequent reactions with OH radicals and other oxidants results in the formation of secondary pollutants, such as phytotoxic trichloroacetic acid (TCA), which are then delivered by the air or rain into the neighbouring ecosystems of various vegetation zones. Biomonitoring investigations in the catchment area of the Caspian Sea have revealed that differences in pollution levels in the southern Russian area between the Black Sea and the Caspian Sea, resulting from TCA originating in the atmosphere, are attributable to climatic conditions and the geographical position of the measuring sites. ©     

Terrestrial water cycle and the impact of climate change

The terrestrial water cycle and the impact of climate change are critical for agricultural and natural ecosystems. In this paper, we assess both by running a macro-scale water balance model under a baseline condition and 2 General Circulation Model (GCM)-based climate change scenarios. The results show that in 2021-2030, water demand will increase worldwide due to climate change. Water shortage is expected to worsen in western Asia, the Arabian Peninsula, northern and southern Africa, northeastern Australia, southwestern North America, and central South America. A significant increase in surface runoff is expected in southern Asia and a significant decrease is expected in northern South America. These changes will have implications for regional environment and socioeconomics.     

Preliminary assessment of risk of ozone impacts to maize (Zea mays) in southern Africa

Surface ozone concentrations in southern Africa exceed air quality guidelines set to protect agricultural crops. This paper addresses a knowledge gap by performing a preliminary assessment of potential ozone impacts on vegetation in southern African. Maize (Zea mays L.) is the receptor of interest in the main maize producing countries, i.e. South Africa, Zambia and Zimbabwe. Surface ozone concentrations are estimated for the growing season (October to April) using photochemical modelling. Hourly mean modelled ozone concentrations ranged between 19.7 and 31.2 ppb, while maximums range between 28.9 and 61.9 ppb, and are near 30 ppb over South Africa and Zambia, while in Zimbabwe, they exceed 40 ppb and translate into monthly AOT40 values of over 3,000 ppb h in five of the seven months of the growing season. This study suggests that surface ozone may pose a threat to agricultural production in southern African, particularly in Zimbabwe.     

Biodegradation of chlorinated solvents in a water unsaturated topsoil

In order to investigate topsoils as potential sinks for chlorinated solvents from the atmosphere, the degradation of trichloromethane (CHCl(3)), 1,1,1-trichloroethane (CH(3)CCl(3)), tetrachloromethane (CCl(4)), trichloroethene (C(2)HCl(3)) and tetrachloroethene (C(2)Cl(4)) was studied in anoxic laboratory experiments designed to simulate denitrifying conditions in water unsaturated topsoil. Active denitrification was demonstrated by measuring the release of 15N in N(2) to the headspace from added 15N labeled nitrate. The degradation of chlorinated aliphatic compounds was followed by measuring their concentrations in the headspace above the soil.The headspace concentrations of all the chlorinated solvents except CH(3)CCl(3) were significantly (P相似文献   

Establishing the propensity for dioxin formation using a plume temperature model for medical waste incinerator emissions in developing countries

Air pollution control devices (APCDs) are not compulsory for medical waste incinerators (MWIs) in developing countries. In South Africa, combustion gases are usually vented directly to the atmosphere at temperatures greater than the formation temperature of dioxin. The possibility of dioxin formation outside the incinerator stack has been hypothesized. A plume model has been developed and tested in the wind tunnel with a scale model of an incinerator stack. The plume temperature and trajectory predictions of the plume model were verified within a +/- 3% experimental accuracy. Using South African data, the plume model predicts that the residence time of gases in the temperature range of 150-450 degrees C in a plume is 1.3 sec on average for 5% of a year (18 days) at meteorological conditions resulting in wind speeds of less than 1 m/sec. Two published dioxin formation models were used to assess the probability of dioxin formation in the plume. The formation models predict that the average polychlorinated dibenzodioxins/furans (PCDD/Fs) formed in the plume will exceed the stack emission regulations in South Africa of 0.2 ng/Nm3 toxic equivalent quotient (TEQ) by between 2 and 40 times. The calculated concentrations do not include additional gaseous PCDD/F compounds that may be formed at high-temperature post-combustion zones through pyrosynthesis mechanisms.     

Review of concentrations and chemistry of trichloroacetate in the environment

This paper reviews the concentrations of trichloroacetate (TCA) in the atmosphere-plant-soil system. Data originate mainly from Europe. The median TCA concentration in rainwater and canopy drip decreased until 1995. From then the median TCA concentration in rainwater remains rather constant while for canopy drip later data are not available. The same seems to hold for concentrations in air although a very limited data set is available. The median concentrations in coniferous needles and groundwater are constant for the period observed. The median TCA concentrations in soil decreased until 1992 and then remained constant.The TCA formation from chlorinated solvents in the atmosphere may explain a substantial percentage of the TCA amount in the atmosphere. The TCA concentrations in rainwater and canopy drip indicate that there will be other sources contributing to 10-50%. Waste incineration, biomass burning and natural formation in the marine boundary layer are potential candidate sources of TCA, but nothing can be said as yet on their TCA emission rates. Anthropogenic emissions of chlorine could also be a source.TCA can be formed from chlorinated solvents by biota. However, for coniferous trees the uptake of TCA from soil may be the predominant route. Biotic and abiotic reactions can cause to formation of TCA in soil, but also formation of TCA from chlorinated solvents by biota that excrete TCA, may contribute. Mass balance calculations of the bioactive soil top layer show that the production rate of TCA in certain soil types could be substantial. The mass balance calculations could not distinguish between natural and anthropogenic sources in soil.     

Organic acids in continental background aerosols

With a newly developed method aerosol samples from three distinctly different continental sites were analyzed: an urban site (Vienna), a savanna site in South Africa (Nylsvley Nature Reserve, NNR) and a free tropospheric continental background site (Sonnblick Observatory, SBO). In all samples a range of monocarboxylic acids (MCAs) and dicarboxylic acids (DCAs) has been identified and quantified. The three most abundant MCAs in Vienna were the C18, C16 and C14 acids with concentrations of 66, 45 and 36 ng m^-3, respectively. At the mid tropospheric background site (SBO) the three most abundant MCAs were the C18, C16 and C12 acid. For the DCAs at all three sites oxalic, malonic and succinic acid were the dominant compounds. For some individual compounds an information about the sources could be obtained. For example the determined unsaturated MCAs in South Africa appear to result from biogenic sources whereas in Vienna those acids are considered to be derived from combustion processes. Oxalic and glyoxalic acid appear to have a free tropospheric air chemical source. The relative high amounts at SBO in comparison to Vienna can only be explained by secondary formation of oxalic acid in the atmosphere.     

Climatic mapping to identify high-risk areas for Cylindrocladium quinqueseptatum leaf blight on eucalypts in mainland South East Asia and around the world

Cylindrocladium quinqueseptatum is a pathogen on a wide range of hosts. It affects at least 20 species of eucalypts and is an important causal agent of leaf blight of Eucalyptus camaldulensis in central and southern Vietnam. Results from previous studies and observations of broadscale infection patterns in mainland South East Asia were used to derive simple rules (i.e. mean minimum temperature of coldest month > or =16 degrees C and mean annual precipitation > or =1400 mm) to identify locations which are likely to have a high risk of C. quinqueseptatum leaf blight (CqLB). Climatic mapping programs, which include interpolated climatic data estimated for numerous locations, were used to map these high risk areas in Africa, Australia and Latin America as well as in South East Asia. The predicted high-risk areas included several regions where CqLB has already been reported and the maps generated suggested other areas which may be at risk under present climatic conditions given the presence of C. quinqueseptatum and susceptible hosts. Some simple climate change scenarios were also used to suggest areas in mainland South East Asia which may become vulnerable to CqLB over the next 50 years. It is concluded that climatic mapping programs can assist the broadscale evaluation of risk of CqLB infections, although it is recognised that more detailed models and survey information are also needed.     

Removal of methyl chloroform in a coastal salt marsh of eastern China

The atmospheric burden of methyl chloroform (CH(3)CCl(3)) is still considerable due to its long atmospheric lifetime, although CH(3)CCl(3) emissions have declined considerably since it was included into the Montreal Protocol. Moreover, CH(3)CCl(3) emissions are used to estimate hydroxyl radical (OH) levels, trends, and hemispheric distributions, and thus the mass balance of the trace gas in the atmosphere is critical for characterizing OH concentrations. Salt marshes may be a potential sink for CH(3)CCl(3) due to its anoxic environment and abundant organic matter in sediments. In this study, seasonal dynamics of CH(3)CCl(3) fluxes were measured using static flux chambers from April 2004 to January 2005, along an elevational gradient of a coastal salt marsh in eastern China. To estimate the contribution of higher plants to the gas flux, plant aboveground biomass was experimentally harvested and the flux difference between the treatment and the intact was examined. In addition, the flux was analyzed in relation to soil and weather conditions. Along the elevational gradient, the salt marsh generally acted as a net sink of CH(3)CCl(3) in the growing season (from April to October). The flux of CH(3)CCl(3) ranged between -3.38 and -32.03 nmol m(-2)d(-1) (positive for emission and negative for consumption), and the maximum negative rate occurred at the cordgrass marsh. However, the measurements made during inundation indicated that the mudflat was a net source of CH(3)CCl(3). In the non-growing season (from November to March), the vegetated marsh was a minor source of CH(3)CCl(3) when soil was frozen, the emission rate ranging from 3.43 to 7.77 nmol m(-2)d(-1). However, the mudflat was a minor sink of CH(3)CCl(3) whether it was frozen or not in the non-growing season. Overall, the coastal salt marsh in eastern China was a large sink for the gas, because the magnitude of consumption rate was lager than that of emission, and because the duration of the growing season was longer than that of the non-growing season. Plant aboveground biomass had a great effect on the flux. Comparative analysis showed that the direction and magnitude of the effect of higher plants on the flux of CH(3)CCl(3) depended on timing of sampling vegetation type. In the growing season the plant biomass decreased the gas flux and acted as a large sink of the gas, whereas it presented as a minor source in the non-growing season. However, the mechanism underlying plant uptake process is not clear. The CH(3)CCl(3) flux was positively related to the dissolved salt concentration and organic matter content in soil, as well as light intensity, but it was negatively related to soil temperature, sulfate concentrations, and initial ambient atmospheric concentrations of CH(3)CCl(3). Our observations have important implications for estimation of the tropospheric lifetime of CH(3)CCl(3) and global OH concentration from the global budget concentration of CH(3)CCl(3).     

Spatial distribution of atmospheric PAHs and PCNs along a north-south Atlantic transect

Ship-board air samples collected between The Netherlands and South Africa in January-February 2001 were analysed for polycyclic aromatic hydrocarbons (PAHs) and polychlorinated naphthalenes (PCNs). The highest PAH concentrations occurred in the European samples, and in samples close to West Africa and South Africa. Consistently low PAH concentrations were measured in the southern hemisphere open ocean samples (190-680 pg/m3). The highest PCN concentrations occurred in the European samples, but high values were also detected off the West African coast, and in the sample taken closest to South Africa. Data are presented for diurnal cycles taken in the remote South Atlantic. The day:night ratios of phenanthrene, 1-methylphenanthrene and fluoranthene were typically approximately 1.5-2.5:1. The mechanism(s) causing this observation is/are not understood at present, but dynamic environmental process(es) is/are implicated.     

Historical record of polycyclic aromatic hydrocarbons (PAHs) and spheroidal carbonaceous particles (SCPs) in marine sediment cores from Admiralty Bay, King George Island, Antarctica

This paper describes the first results of polycyclic aromatic hydrocarbons (PAHs) and spheroidal carbonaceous particles (SCPs) in sediment cores of Admiralty Bay, Antarctica. These markers were used to assess the local input of anthropogenic materials (particulate and organic compounds) as a result of the influence of human occupation in a sub-Antarctic region and a possible long-range atmospheric transport of combustion products from sources in South America. The highest SCPs and PAHs concentrations were observed during the last 30 years, when three research stations were built in the area and industrial activities in South America increased. The concentrations of SCPs and PAHs were much lower than those of other regions in the northern hemisphere and other reported data for the southern hemisphere. The PAH isomer ratios showed that the major sources of PAHs are fossil fuels/petroleum, biomass combustion and sewage contribution generally close to the Brazilian scientific station.     

Factors on the formation of disinfection by-products MX, DCA and TCA by chlorination of fulvic acid from lake sediments

[3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone] (MX) and chlorinated acetic acids such as dichlorinated acetic acid (DCA) and trichlorinated acetic acid (TCA) have always been the focus of disinfection by-products (DBPs) studies. In order to find out the influences of reaction time, TOC, chlorine dose, pH and temperature on the formation of MX, DCA and TCA, we extracted fulvic acid (FA) from the sediment of Tai Lake, and conducted simulated chlorination of samples rich in FA. Results showed positive relationship between TOC and the yields of MX, DCA and TCA. But the influences of pH, chlorine dose, reaction time, and temperature are quite complex. The optimal chlorination condition for the formation of MX is pH = 2, T = 45 degrees C, C/Cl2 = 1/4, t = 12 h. Lower pH, longer time, greater chlorine dose can result in greater yield of both DCA and TCA, and there is a strong linear relationship between the formation of DCA and TCA.     

BETR North America: a regionally segmented multimedia contaminant fate model for North America

We present the Berkeley-Trent North American contaminant fate model (BETR North America), a regionally segmented multimedia contaminant fate model based on the fugacity concept. The model is built on a framework that links contaminant fate models of individual regions, and is generally applicable to large, spatially heterogeneous areas. The North American environment is modeled as 24 ecological regions, within each region contaminant fate is described using a 7 compartment multimedia fugacity model including a vertically segmented atmosphere, freshwater, freshwater sediment, soil, coastal water and vegetation compartments. Inter-regional transport of contaminants in the atmosphere, freshwater and coastal water is described using a database of hydrological and meteorological data compiled with Geographical Information Systems (GIS) techniques. Steady-state and dynamic solutions to the 168 mass balance equations that make up the linked model for North America are discussed, and an illustrative case study of toxaphene transport from the southern United States to the Great Lakes Basin is presented. Regionally segmented models such as BETR North America can provide a critical link between evaluative models of long-range transport potential and contaminant concentrations observed in remote regions. The continent-scale mass balance calculated by the model provides a sound basis for evaluating long-range transport potential of organic pollutants, and formulation of continent-scale management and regulatory strategies for chemicals.     

Environmental risk assessment of airborne trichloroacetic acid--a contribution to the discussion on the significance of anthropogenic and natural sources

In environmental risk assessments the question has to be answered, whether risk reduction measures are necessary in order to protect the environment. If the combination of natural and anthropogenic sources of a chemical substance leads to an unacceptable risk, the man-made emissions have to be reduced. In this case the proportions of the anthropogenic and natural emissions have to be quantified. Difficulties and possible solutions are discussed in the scope of the OECD- and EU-risk assessments of trichloroacetic acid (TCA) and tetrachloroethylene.In the atmosphere, TCA is formed by photo-oxidative degradation of tetrachloroethylene (PER) and 1,1,1-trichloroethane. The available data on atmospheric chemistry indicate that tetrachloroethylene is the more important pre-cursor. With its high water solubility and low volatility, TCA is adsorbed onto aerosol particles and precipitated during rainfalls. Extended monitoring in rainwater confirmed the global distribution of airborne TCA. TCA reaches soils by dry and wet deposition. In addition formation of TCA from tetrachloroethylene in plants was observed. Consequently, high concentrations were detected in needles, leaves and in forest soil especially in mountain regions.The effect assessment revealed that plants exposed via soil are the most sensitive species compared to other terrestrial organisms. A PNECsoil of 2.4 microg/kg dw was derived from a long-term study with pine and spruce seedlings. When this PNEC is compared with the measured concentrations of TCA in soil, in certain regions a PEC/PNEC ratio >1 is obtained. This clearly indicates a risk to the terrestrial ecosystem, with the consequence that risk reduction measures are deemed necessary.To quantify the causes of the high levels of TCA in certain soils, and to investigate the geographical extent of the problem, intensive and widespread monitoring of soil, air and rainwater for TCA and tetrachloroethylene would be necessary to be able to perform a full mass balance study at an appropriate number of sites. In addition, measurements of the 14C content in TCA isolated from soil could clarify whether a significant proportion of the TCA occurs from natural sources. The possible formation of TCA in soil can also be tested by incubation of isotope enriched inorganic chloride with subsequent mass spectrometry of TCA.     

Trichloroacetic acid cycling in Sitka spruce saplings and effects on sapling health following long term exposure

Trichloroacetic acid (TCA, CCl(3)COOH) has been associated with forest damage but the source of TCA to trees is poorly characterised. To investigate the routes and effects of TCA uptake in conifers, 120 Sitka spruce (Picea sitchensis (Bong.) Carr) saplings were exposed to control, 10 or 100 microg l(-1) solutions of TCA applied twice weekly to foliage only or soil only over two consecutive 5-month growing seasons. At the end of each growing season similar elevated TCA concentrations (approximate range 200-300 ng g(-1) dwt) were detected in both foliage and soil-dosed saplings exposed to 100 microg l(-1) TCA solutions showing that TCA uptake can occur from both exposure routes. Higher TCA concentrations in branchwood of foliage-dosed saplings suggest that atmospheric TCA in solution is taken up indirectly into conifer needles via branch and stemwood. TCA concentrations in needles declined slowly by only 25-30% over 6 months of winter without dosing. No effect of TCA exposure on sapling growth was measured during the experiment. However at the end of the first growing season needles of saplings exposed to 10 or 100 microg l(-1) foliage-applied TCA showed significantly more visible damage, higher activities of some detoxifying enzymes, lower protein contents and poorer water control than needles of saplings dosed with the same TCA concentrations to the soil. At the end of each growing season the combined TCA storage in needles, stemwood, branchwood and soil of each sapling was <6% of TCA applied. Even with an estimated half-life of tens of days for within-sapling elimination of TCA during the growing season, this indicates that TCA is eliminated rapidly before uptake or accumulates in another compartment. Although TCA stored in sapling needles accounted for only a small proportion of TCA stored in the sapling/soil system it appears to significantly affect some measures of sapling health.     

Flow behavior and residual saturation formation of liquid carbon tetrachloride in unsaturated heterogeneous porous media

The formation of residual, discontinuous nonaqueous phase liquids (NAPLs) in the vadose zone is a process that is not well understood. To obtain data that can be used to study the development of a residual NAPL saturation in the vadose zone and to test current corresponding models, detailed transient experiments were conducted in intermediate-scale columns and flow cell. The column experiments were conducted to determine residual carbon tetrachloride (CCl(4)) saturations of two sands and to evaluate the effect of CCl(4) vapors on the water distribution. In the intermediate-scale flow cell experiment, a rectangular zone of the fine-grained sand was packed in an otherwise medium-grained matrix. A limited amount of CCl(4) was injected from a small source and allowed to redistribute until a pseudo steady state situation had developed. A dual-energy gamma radiation system was used to determine fluid saturations at numerous locations. The experiments clearly demonstrated the formation of residual CCl(4) saturations in both sands. Simulations with an established multifluid flow simulator show the shortcomings of current relative permeability-saturation-capillary pressure (k-S-P) models. The results indicate that nonspreading behavior of NAPLs should be implemented in simulators to account for the formation of residual saturations.     

Gas-phase reaction of CCl2F2 (CFC-12) with methane

Gas-phase reaction of CFC-12 (CCl2F2) with methane was carried out in a plug flow reactor over the temperature range of 873-1123 K. The major organic halocarbons formed during the reaction were C2F4, C2H2F2, CHClF2, CH3Cl, C3H2F6 and CCl3F. The formation of all products except C2H2F2 decreased with temperature, while the selectivity to C2H2F2 (difluoroethylene) increased with temperature and reached approximately 80% at 1123 K. Under these reaction conditions, methane acts as hydrogen and carbon source, resulting in the formation of an unsaturated C2 hydrofluorocarbon from two C1 precursors.     

Effect of biogenic iron species and copper ions on the reduction of carbon tetrachloride under iron-reducing conditions

In this study, the cell-mediated and abiotic reduction of carbon tetrachloride (CCl(4)) by biogenic iron species produced from the reductive dissolution of ferrihydrite in the presence of Geobacter sulfurreducens and copper ions (Cu(II)) were investigated. 9,10-Anthraquinone-2,6-disulfonate (AQDS), serving as a surrogate of natural organic matters and an electron shuttling compound, was added to enhance the efficiency of biological reduction of the solid Fe(III) minerals. G. sulfurreducens drove the reduction of CCl(4), primarily through the formation of biogenic surface-bound iron species produced from the reductive dissolution of ferrihydrite, in the presence of 10microM AQDS. The pseudo-first-order rate constant (k(obsCT)) for CCl(4) transformation in the presence of ferrihydrite was 3.0 times higher than that resulting from the use of G. sulfurreducens alone. Addition of 0.5mM Cu(II) slightly inhibited both the growth of G. sulfurreducens and the production of biogenic Fe(II). However, the k(obsCT) values for CCl(4) transformation in ferrihydrite suspensions containing G. sulfurreducens and 0.3-0.5mM Cu(II) were 2.1-4.2 times higher than that observed in the absence of Cu(II). X-Ray powder diffraction analysis indicated that the added Cu(II) reacted with the biogenic Fe(II) ions to produce catalytic cuprous ions (Cu(I)) and secondary iron oxide minerals such as magnetite and goethite, resulting in accelerating the chemical transformation efficiency and rate of CCl(4) under iron-reducing conditions.