Estimation of the volatilization of organic compounds from soil surfaces

Several simple models for the estimation of the half-life (t(1/2)) for the depletion of an organic chemical from a soil surface to air were examined. For moist surfaces, two models are proposed: the first requires knowledge of the soil/organic carbon partition coefficient (K(oc)) and the Henry's law constant (H) and the second the vapor pressure (P(s)) of the chemical involved. Due to uncertainties in the experimental K(oc) values those ones predicted by the group-contribution model of Meylan et al. [Environ. Sci. Technol. 26 (1992) 1560]-and proposed by the U.S. Environmental Protection Agency (EPA)-should be used. If reliable experimental P(s) values are not available, the first model is proposed, where in cases when H values are not available, predicted ones by the Bond-Contribution method of Meylan and Howard [Environ. Toxicol. Chem. 10 (1991) 1283]-and also proposed by EPA-can be used. In general, the agreement of the predicted t(1/2) values with the measured ones is within a factor of 3-5. Similar expressions, but with somewhat poorer results, are presented for dry field soils. In all cases, the obtained results represent a substantial improvement over those obtained with the currently used Dow method: t(1/2) = 1.58 x 10(-8)((K(oc) x S)/P(S)), where S is the solubility of the compound in water.     

Biomineralization rates of 14C-labelled organic chemicals in aerobic and anaerobic suspended soil

The formation of ¹⁴CO₂ from 13 ¹⁴C-labelled organic chemicals in aerobic and anaerobic suspended soil was determined. After 5 days at 35°C, ¹⁴CO₂ was between 70.1% (urea, anaerobic) and < 0.1% (2,6-dichlorobenzonitrile and hexachlorobenzene, aerobic and anaerobic) of the ¹⁴C initially applied.     

Volatilization rates of intermediate and low volatility chemicals from water

This paper reports laboratory methods for measuring the gas and liquid phase mass transfer coefficients and volatilization rate constants of intermediate and low volatility compounds and proposes a method for calculating the volatilization rate constants of these types of compounds in the environment.     

Reaction rates and intermediates of chlorinated organic compounds in water and soil

Degradation reactions of thirteen chlorinated organic compounds were investigated in a water system and a water-soil system. Three compounds were degraded following the first order rate equation regardless of pH, and five compounds were degraded following the second order rate equation with a concentration of hydroxide ion in alkaline solution.The reaction rate constants and the activation energies of the reactions were obtained, and the intermediates were determined quantitatively for the eight compounds.From the result of the degradation of 1,1,1-trichloroethane in the water-soil system, it was found that 1,1,1 trichloroethane did not react on the soil surface and only reacted in the water phase.     

Estimating biotransformation rate constants of organic chemicals from modeled and measured elimination rates.

In this study, biotransformation rate constants are estimated for a large set of organic compounds. Biotransformation (km) is considered part of the total elimination, further consisting of physico-chemical elimination to water (kw), depuration by feces (kf) and growth dilution (gamma). Existing models are used to estimate kw and kf, and gamma. The difference between measured elimination rate constants and the sum of predicted elimination rate constants for water, feces and growth indicates the ration of biotransformation in the total elimination. In all examined animal classes, polycyclic aromatic hydrocarbons seem to be metabolized at an intermediate rate. Because of the relative low hydrophobicity of some of the studied compounds, their physico-chemical elimination rate constant is relatively high, and the relative contribution of metabolism to total elimination of these compounds is therefore relatively low. Fish seem to be capable of metabolizing chlorodibenzo-p-dioxins and -furans, DDT, chloroanilines and phenol.     

An alternative method for predicting organic solute volatilization rates under gas and liquid turbulence

A method for predicting organic compound volatilization rates under turbulent liquid and gas conditions is developed. The reference compounds are classified according to their physico-chemical properties. The mass transfer coefficient (K(OL)) ratios for organic solutes to the reference compounds are constant for a wide range of environmental conditions, including liquid or air turbulence, or both at once. The obtained results indicate that when the environmental conditions are the same the determination of the volatilization rates is strongly dependent on the solute properties and the chemical structure. The presented method can more effectively estimate the volatilization rates of the solutes than the traditional one under various environmental conditions especially for low volatility solutes. The advantages and disadvantages of the traditional method are also discussed.     

Trace organic chemicals contamination in ground water recharge

Population growth and unpredictable climate changes will pose high demands on water resources in the future. Even at present, surface water is certainly not enough to cope with the water requirement for agricultural, industrial, recreational and drinking purposes. In this context, the usage of ground water has become essential, therefore, their quality and quantity has to be carefully managed. Regarding quantity, artificial recharge can guarantee a sustainable level of ground water, whilst the strict quality control of the waters intended for recharge will minimize contamination of both the ground water and aquifer area. However, all water resources in the planet are threatened by multiple sources of contamination coming from the extended use of chemicals worldwide. In this respect, the environmental occurrence of organic micropollutants such as pesticides, pharmaceuticals, industrial chemicals and their metabolites has experienced fast growing interest. In this paper an overview of the priority and emerging organic micropollutants in the different source waters used for artificial aquifer recharge purposes and in the recovered water is presented. Besides, some considerations regarding fate and removal of such compounds are also addressed.     

Kinetics of peat soil dissolved organic carbon release from bed sediment to water. Part 1. Laboratory simulation

Temporary water reservoirs built upon peat soil may exhibit water quality impairment from elevated dissolved organic carbon (DOC). Microbiological decay of the organic carbon in the bed with subsequent release produces "tea" colored water which may require treatment prior to use. This paper describes laboratory experiments designed to obtain data on the release process of DOC from soils containing 0.65%, 10% and 19% carbon. Parallel experiments with and without sodium azide treatment clearly distinguished the initial release of a porewater residual fraction and the microbial produced fraction. A one to two day quick-release DOC fraction, which ranges from 28% to 50%, first emerged from the bed, Step-1. This was followed by a constant rate of DOC production over four weeks, Step-2. The Step-2 average production rates were 3.4, 12, and 31 mg DOC/kg(dry)/day for the respective soils and increased as soil carbon content increased. The inorganic carbon (IC) behaved oppositely; its rate of production decreased with increasing soil carbon. A consistent and simple rate equation described the Step-2 DOC production process. This and other evidence obtained provided the basis for developing a mathematical model that couples both steps of the bed-to-water DOC release chemodynamics. The model is presented in a companion paper (Part-2).     

Relationship between water solubility of organic chemicals and their bioaccumulation by the alga

This paper reports the bioaccumulation of 34 organic chemicals in and on the green alga and their relationship to water solubility.     

Effect of a cationic surfactant on the volatilization of PAHs from soil

Purpose

Cationic surfactants are common in soils because of their use in daily cosmetic and cleaning products, and their use as a soil amendment for the mitigation and remediation of organic contaminated soils has been proposed. Such surfactant may affect the transfer and fate of organic contaminants in the environment. This study investigated the effect of a cationic surfactant, dodecylpyridinium bromide (DDPB), on the volatilization of polycyclic aromatic hydrocarbons (PAHs) from a paddy soil.

Materials and methods

The volatilization of PAHs from moist soil amended with different concentrations of DDPB was tested in an open system. The specific effects of DDPB on the liquid?Cvapor and solid?Cvapor equilibriums of PAHs were separately investigated in closed systems by headspace analysis.

Results and discussion

DDPB affects both liquid?Cvapor and solid?Cvapor processes of PAHs in soil. At DDPB concentrations below the critical micelle concentration (CMC), movement of PAHs from the bulk solution to the gas?Cliquid interface appeared to be facilitated by interaction between PAHs and the surfactant monomers adsorbed at the gas?Cliquid interface, promoting the volatilization of PAHs from solution. However, when DDPB was greater than the CMC, volatilization was inhibited due to the solubilization of PAHs by micelles. On the other hand, the formation of sorbed surfactant significantly inhibited the solid?Cvapor volatilization of PAHs.

Conclusions

The overall effect of the two simultaneous effects of DDPB on liquid?Cvapor and solid?Cvapor processes was a decreased volatilization loss of PAHs from soil. Inhibition of PAH volatilization was more significant for the soil with a lower moisture content.     

Plant uptake of non-ionic organic chemicals from soils

Methodologies utilizing simple properties of chemicals - half-life (T_1/2), log octanol-water partition coefficient (log K_ow) and Henery's Law constant (Hc) - are developed to screen organic chemicals for potential plant uptake.     

Laboratory screening of distribution,conversion and mineralization of chemicals in the soil-plant-system and comparison to outdoor experimental data

A laboratory screening method is presented which yields data on residue disappearance and conversion of ¹⁴C-labelled chemicals in the soil-plant-system. For 11 chemicals it is shown that a relative prediction resulting in a correct ranking for outdoor long-term behaviour is possible.     

Outdoor experiments on enhanced volatilization by venting of kerosene component from soil

The effect of soil properties on the retention of kerosene in soils, at equilibrium and under venting, was studied. Eleven soils were studied, which represent a wide range of chemical properties and mechanical composition. The retention of kerosene in dry soils ranges from 3.5 to 18.1 mL/(100 g), and was related linearly to clay, silt and organic matter (OM) contents. A coarsely-aggregated dry vertisol (2–5 mm aggregates) retained half as much kerosene as its finely-aggregated (<2 mm) counterpart. Moisture content had a strong inverse effect on kerosene retention. The soil factors that inversely affected kerosene retention also enhanced kerosene stripping by venting. Of these, soil aggregation and porosity were the most important. In addition, kerosene volatilized faster and more completely from an initially moist soil, as compared with an initially dry soil. Differential volatilization of lighter components of kerosene changed the chemical composition of the residue in the soil substantially, as compared with the initial composition.     

Influence of methanol on retention of hydrophobic organic chemicals in soil leaching column chromatography

The influence of methanol in methanol-water mixed eluents on the capacity factor (k'), an important parameter which could depict leaching potential of hydrophobic organic chemicals (HOCs) in soil leaching column chromatography (SLCC), was investigated. Two reference soils, GSE 17201 obtained from Bayer Landwirtschaftszentrum, Monheim, Germany and SP 14696 from LUFA, Spencer, Germany, were used as packing materials in soil columns, and isocratic elution with methanol-water mixtures at different volume fractions of methanol (phi) were tested. Short-term exposure of the column (packed with the GSE 17201 soil) to the eluents increased solute retention by a certain (23% log-unit) degree evaluated through a correlation with the retention on the same soil column but unpreconditioned by methanol-containing eluents. Long-term exposure of soil columns to the eluents did not influence the solute retention. A log-linear equation, log k' = log k'(w) - S(phi), could well and generally describe the retention of HOCs in SLCC. For the compounds of homologous series, logk'(w) had good linear relationship with S, indicating the hydrophobic partition mechanism existing in the retention process.     

Leaching kinetics of water soluble organic carbon (WSOC) from upland soil.

The kinetics of the leaching process of Water Soluble Organic Carbon (WSOC) from an upland soil were studied in a column leaching experiment. The pattern of the leaching curve indicated multiphasic release kinetics. A conceptual model was proposed to divide capillary and gravitational pores. The translocation of organic carbon in soil during leaching occurs in four sequential steps. 1) degradation of insoluble organic carbon to form WSOC; 2) desorption into capillary pore water; 3) diffusion towards gravitation pore water; and 4) leaching by convection flow. The overall kinetics of the leaching process can be depicted using an equation with three additive terms for degradation, desorption/diffusion, and convection, respectively.     

中国地表饮用水水源地有机类内分泌干扰物污染现况分析

有机类内分泌干扰物(EDCs)是一类对人类和生物内分泌系统产生干扰,并可造成其紊乱的特殊外来物质,对人类和生物健康有极大的危害.以与人类生活密切相关的地表饮用水水源地中的有机类EDCs为研究重点,对中国目前地表饮用水水源地EDCs污染状况、污染物种类及其来源及可能的污染途径进行了评述.目前,中国各地区地表饮用水水源地均有有机类EDCs检出.其中以有机氯农药六六六及其异构体、DDT及其代谢产物和多氯联苯检出率最高,且某些地区检测浓度相当高,主要来源是农药使用和污水排放.国内外对地表饮用水水源地EDCs突发污染事件的研究均较少,应引起高度重视.     

Concentrations of Synthetic organic chemicals in leachate from a municipal landfill

A study on the concentrations of synthetic organic chemicals in leachate from the municipal landfill of Lake Charles, Louisiana, was conducted from June 1987 through March 1989. The primary objective of this study was to provide information on the concentrations of synthetic organics in leachate from a typical municipal landfill. Leachate analyses yielded the presence of a variety of synthetic organic compounds at wide ranges in concentration. These compounds are potentially dangerous to human health.     

Quantifying the sorption of organic chemicals on sediments

The use of a reference compound to quantify the sorption of nonpolar organic chemicals is proposed. This is because organic carbon normalized sorption coefficients (K_OC) do appear to be dependent on the type of sediment, and are thus not generally applicable to characterize the sorption properties of chemicals. Therefore, in this paper the hypothesis that nonpolar chemicals sorb in a constant ratio, independent of the sediment, has been investigated. Evidence for this hypothesis is shown with data from the literature. This enables one to compare sorption properties of nonpolar compounds on different sediments, if the differences between the sediments are normalized with a reference chemical rather than with the organic carbon content. Sediments with an organic carbon content of less than 0.1% seem to be unsuitable, because the compounds do not sorb mainly on the organic carbon, but also on other parts of the sediment. Sorption coefficients of compounds with aqueous solubilities in the μg per liter range or octan-1-ol water partition coefficients of more than 10⁵ are strongly influenced by the experimental techniques used. For these compounds the sorption coefficients measured by different techniques are less comparable. To enable comparison of sorption coefficients of hydrophobic chemicals, the use of a chlorobenzene as a reference compound in sorption experiments is suggested.     

Correlation between the bioconcentration potential of organic environmental chemicals in humans and their n-octanol/water partition coefficients

A quantitative relationship was found to exist between the lipophilicity (n-octanol/water partition coefficient) of pentachlorophenol, dieldrin, hexachlorobenzene, 2,3,7,8-tetrachlorodibenzo-p-dioxin, Σ DDT, polychlorinated biphenyls, α-, β-, γ- and δ -hexachlorocyclohexane and their bioconcentration factor (BCF) in human adipose tissue. The equations were used to predict the bioconcentration factors of some chlorinated aromatic chemicals.