A wind tunnel for measuring the gaseous losses of environmental chemicals from the soil/plant system under field-like conditions

Volatilization from treated areas is a major source of pesticide residues in air, fog, and rain. This may lead to long-range transport of pesticide residues to remote areas. Up to now most information on pesticide volatilization has come from laboratory experiments under controlled conditions. A new system has been designed and developed to measure the volatile losses of¹⁴C-labelled chemicals after application; the method compares with agricultural practice of treating soils or plants grown in lysimeters. Sensitive analytical methods guarantee a distinction between residues of unchanged pesticide, its metabolites or¹⁴CO₂ as a mineralization product released into the air.     

Degradation of chlorpyrifos and its hydrolysis product, 3,5,6‐trichloro‐2‐pyridinol,in soil

Abstract

The degradation of ¹⁴C‐chlorpyrifos and its hydrolysis product, 3,5,6‐trichloro‐2‐pyridinol (TCP), was investigated in soil in laboratory experiments. Between 12 and 57% of the applied chlorpyrifos persisted in a variety of agricultural soils after a 4‐week incubation. Concentrations of TCP present in these soils ranged from 1 to 34% of the applied dose. Two patterns of persistence were observed. In some soils, significant quantities of TCP and soil‐bound residues were produced, but little ¹⁴CO₂. In other soils, neither TCP nor soil‐bound residues accumulated, but large quantities of ¹⁴CO₂ were evolved. Direct treatment of fresh samples of each of these soils with ¹⁴C‐TCP resulted in rapid mineralization of TCP to ¹⁴CO₂ only in those soils in which TCP had not accumulated after chlorpyrifos treatment. The rapid mineralization of TCP in these soils was microbially mediated, but populations of soil microorganisms capable of using TCP as a sole carbon‐energy source were not detected.     

Comparative studies of the fate of atrazine‐14C and pentachlorophenol‐14C in various laboratory and outdoor soil‐plant systems

Abstract

Mass balance and fate of atrazine‐ ¹⁴C and pentachlorophenol‐ ¹⁴C (PCP‐ ¹⁴C) were studied in short‐term tests in a closed aerated laboratory soil‐plant system, using two concentrations in soil and two plant species, as well as under outdoor conditions for one vegetation period. In the laboratory, for both pesticides bioaccu‐mulation factors of radiocarbon taken up by the roots into plants were low. They were higher for lower (1 ppm) than for higher soil concentrations (6 ppm for atra‐zine, 4 ppm for pentachlorophenol) and varied with the plant species. Mineralization to ¹⁴CO₂ in soil was negatively related to soil concentration only for PCP‐ ¹⁴C. Conversion rates in soil including the formation of soil‐bound residues were higher for the lower concentrations of both pesticides than for the higher ones; conversion rates in plants were species‐dependent. In 14 terms of CO₂ formation and of conversion rates, PCP was less persistent in soil than was atrazine. For both pesticides, laboratory data on conversion and mineralization gave a rough prediction of their persistence in soil under long‐term outdoor conditions, whereas bio‐accumulation factors in plants under long‐term outdoor conditions could not be predicted by short‐term laboratory experiments.     

Influence of humic fractions on retention of isoproturon residues in two Moroccan soils

The influence of different fractions of soil organic matter on the retention of the herbicide isoproturon (IPU) has been evaluated. Water and methanol extractable residues of ¹⁴C labeled isoproturon have been determined in two Moroccan soils by β -counting–liquid chromatography. The quantification of bound residues in soil and in different fractions of soil humic substances has been performed using pyrolysis/scintillation-detected gas-chromatography. Microbial mineralization of the herbicide and soil organic matter has been also monitored. Retention of isoproturon residues after 30-days incubation ranged from 22% to 32% (non-extractable fraction). The radioactivity extracted in an aqueous environment was from 20% to 33% of the amount used for the treatment; meanwhile, methanol was able to extract another 48%. Both soils showed quantities of bound residues into the humin fraction higher than humic and fulvic acids. The total amount of residues retained into the organic matter of the soils was about 65 % of non-extractable fraction, and this percentage did not change with incubation time; on the contrary, the sorption rate of the retention reaction is mostly influenced by the clay fraction and organic content of the soil. Only a little part of the herbicide was mineralized during the experimental time.     

Plant availability of bound anilazine residues in a degraded loess soil

Abstract

The relative biological availability of [benzene ring‐U‐¹⁴C] and Ctriazine‐U‐¹⁴C] anilazine for maize plants was studied in a degraded loess soil in a standardized microecosystem. The total uptake of radiocarbon in the course of the 4‐week experiment was 3.1 and 4 % respectively of the radioactivity applied if anilazine was uniformly mixed into the soil immediately before beginning the experiment. However, if anilazine was subjected to a degradation at 65 % of the maximum water holding capacity of the soil and temperatures varying daily between 16 and 27°C for 100 days before the plant experiment then the uptake was reduced to 0.4 or 0.7 % respectively. The uptake from soil with non‐extractable (bound) anilazine residues was similarly low. The mineralization rate of aged and bound anilazine residues was below 0.1 % of the radioactivity applied. Up to 2/3 of the radioactivity present in the soil after the plant experiment remained in the humic fraction.     

Influence of humic fractions on retention of isoproturon residues in two Moroccan soils

The influence of different fractions of soil organic matter on the retention of the herbicide isoproturon (IPU) has been evaluated. Water and methanol extractable residues of (14)C labeled isoproturon have been determined in two Moroccan soils by beta -counting-liquid chromatography. The quantification of bound residues in soil and in different fractions of soil humic substances has been performed using pyrolysis/scintillation-detected gas-chromatography. Microbial mineralization of the herbicide and soil organic matter has been also monitored. Retention of isoproturon residues after 30-days incubation ranged from 22% to 32% (non-extractable fraction). The radioactivity extracted in an aqueous environment was from 20% to 33% of the amount used for the treatment; meanwhile, methanol was able to extract another 48%. Both soils showed quantities of bound residues into the humin fraction higher than humic and fulvic acids. The total amount of residues retained into the organic matter of the soils was about 65 % of non-extractable fraction, and this percentage did not change with incubation time; on the contrary, the sorption rate of the retention reaction is mostly influenced by the clay fraction and organic content of the soil. Only a little part of the herbicide was mineralized during the experimental time.     

Metabolism of 14C‐carbaryl and 14C‐1‐naphthol in moist and flooded soils

Abstract

The metabolism of ¹⁴C‐carbaryl and ¹⁴C‐1‐naphthol in moist and flooded soils was studied in a continuous flow‐through system over a period of 28 days permitting ¹⁴C‐mass balance. The percent distribution of radiocarbon in organic volatiles, carbon dioxide, extractable and non‐extractable (bound) fractions of soils were determined. Organic volatiles could not be detected in both carbaryl and 1‐naphthol treated soils. More of ¹⁴CO₂ (25.6%) was evolved from moist than flooded soil (15.1%) treated with carbaryl. However, the mineralization of ¹⁴C‐1‐naphthol was negligible. The extractable radiocarbon was more in flooded soil (28.9%) than moist soil (5.5%) from carbaryl treatment. Less than one percent was present as parent compound, whereas carbaryl was mainly metabolized to 5‐hydroxy carbaryl in moist soil and to 4‐ and 5‐hydroxy carbaryl in flooded soil. The extractable radiocarbon amounted to 18.2 and 24.3% in moist and flooded soils respectively and the parent compound was less than one percent with 1‐naphthol treatment. Most of the radiocarbon was found as soil bound residues; the formation being more with 1‐naphthol than carbaryl. Humin fraction of the soil organic matter contributed most to soil bound residues of both carbaryl and 1‐naphthol.     

Predicting molybdenum toxicity to higher plants: Influence of soil properties

The effect of soil properties on the toxicity of molybdenum (Mo) to four plant species was investigated. Soil organic carbon or ammonium-oxalate extractable Fe oxides were found to be the best predictors of the 50% effective dose (ED₅₀) of Mo in different soils, explaining > 65% of the variance in ED₅₀ for four species except for ryegrass (26-38%). Molybdenum concentrations in soil solution and consequently plant uptake were increased when soil pH was artificially raised because sorption of Mo to amorphous oxides is greatly reduced at high pH. The addition of sulphate significantly decreased Mo uptake by oilseed rape. For risk assessment, we suggest that Mo toxicity values for plants should be normalised using soil amorphous iron oxide concentrations.     

Toxicity, uptake and metabolism of 4-n-nonylphenol in root cultures and intact plants under septic and aseptic conditions

4-Nonylphenol, a compound with estrogenic activity, has been shown to occur in sewage sludges and effluents of sludge treatment. This, as well as its use in the formulation of pesticides, may result in the contamination of crop plants and may therefore have an impact on the quality of food or feedstuff. The toxicity, uptake and metabolism of 4-n-nonylphenol (4-n-NP) were investigated as¹⁴C-labeled 4-n-NP in root cultures under septical and aseptical conditions and with intact plants grown in containers with soil and aseptically grown in nutrient media. 4-n-NP was toxic to all plant systems tested. The presence of microorganisms and the developmental state of the plant material appeared to have an influence on the EC₅₀ values. 4-n-NP was taken up by the roots and a metabolism to polar compounds was observed in the cases where sufficiently high uptake rates. With intact plants a transport from roots to the shoots was evident. Metabolism in roots changed quantitatively in the presence of microorganisms. The mineralization of 4-n-NP to₁₄CO₂ only occurred with microorganisms.     

Biodegradation of Trifluralin in Harran Soil

Abstract

Degradation of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) was investigated in soils taken from three different locations at Harran region of Turkey under laboratory conditions. Surface (0–10 cm) soils, which were taken from a pesticide untreated field Gürgelen, Harran-1 and Ikizce regions in the Harran Plain, were incubated in biometer flasks for 350 days at 25°C. Ring-UL-¹⁴C-trifluralin was applied at the rate of 2 µg g^?1 with 78.7 kBq radioactivity per 100 g soil flask. Evolved ¹⁴CO₂ was monitored in KOH traps throughout the experiment. Periodically, soil sub-samples were removed and extracted by supercritical fluid extraction (SFE). Unextractable soil-bound ¹⁴C residues were determined by combustion. During the 350 days incubation period 6.6, 5.4, and 3.3% of the applied radiocarbon was evolved as ¹⁴CO₂ from the Harran-1, Gürgelen, and Ikizce soil, respectively. At the end of 350 days the SFE-extractable and bound ¹⁴C-trifluralin residues were 39.0 and 29.2% of the initially applied herbicide in Gürgelen soil. The corresponding values for Harran-1 and Ikizce soils were 36.2, 28.4% and 41.6, 18.5% respectively.     

Fate of 14C‐allylalcohol herbicide in soils and crop residues

Abstract

Residue disappearance and leaching of ¹⁴C‐allyl‐alcohol from different soils were studied in laboratory experiments. Additionally, the uptake of residues by lettuce and carrots was investigated in the greenhouse. In laboratory experiments, residue disappearance and leaching from soils was correlated negatively to the organic matter content. In greenhouse experiments with a sandy loam soil at an application rate normally used in practice, an average of 12.5 % of the applied radioactivity was recovered after an eight day interval between application and sowing. Furthermore, an average of 8 % (sum in soil and plants) of the applied radioactivity was recovered after lettuce or carrot growing. Uptake of residues was higher by carrots than by lettuce, and higher by lettuce roots than by lettuce tops. No bioaccumulation was observed. The residues in soils and plants were, to a high percentage, unextractable and, to a smaller extent, fully water‐soluble products. Unchanged allylalcohol could not be detected by the analytical methods used.     

Fate in soil of 14C-sulfadiazine residues contained in the manure of young pigs treated with a veterinary antibiotic

The fate of ¹⁴C-labeled sulfadiazine (¹⁴C-SDZ) residues was studied in time-course experiments for 218 days of incubation using two soils (A_p horizon of loamy sand, orthic luvisol; A_p horizon of silt loam, cambisol) amended with fresh and aged (6 months) ¹⁴C-manure [40 g kg^?1 of soil; 6.36 mg of sulfadiazine (SDZ) equivalents per kg of soil], which was derived from two shoats treated with ¹⁴C-SDZ. Mineralization of ¹⁴C-SDZ residues was below 2% after 218 days depending little on soil type. Portions of extractable ¹⁴C (ethanol-water, 9:1, v/v) decreased with time to 4–13% after 218 days of incubation with fresh and aged ¹⁴C-manure and both soils. Non-extractable residues were the main route of the fate of the ¹⁴C-SDZ residues (above 90% of total recovered ¹⁴C after 218 days). These residues were high immediately after amendment depending on soil type and aging of the ¹⁴C-manure, and were stable and not remobilized throughout 218 days of incubation. Bioavailable portions (extraction using CaCl₂ solution) also decreased with increasing incubation period (5–7% after 218 days). Due to thin-layer chromatography (TLC), 500 μg of ¹⁴C-SDZ per kg soil were found in the ethanol-water extracts immediately after amendment with fresh ¹⁴C-manure, and about 50 μg kg^?1 after 218 days. Bioavailable ¹⁴C-SDZ portions present in the CaCl₂ extracts were about 350 μg kg^?1 with amendment. Higher concentrations were initially detected with aged ¹⁴C-manure (ethanol-water extracts: 1,920 μg kg^?1; CaCl₂ extracts: 1,020 μg kg^?1), probably due to release of ¹⁴C-SDZ from bound forms during storage. Consistent results were obtained by extraction of the ¹⁴C-manure-soil samples with ethyl acetate; portions of N-acetylated SDZ were additionally determined. All soluble ¹⁴C-SDZ residues contained in ¹⁴C-manure contributed to the formation of non-extractable residues; a tendency for persistence or accumulation was not observed. SDZ's non-extractable soil residues were associated with the soluble HCl, fulvic acids and humic acids fractions, and the insoluble humin fraction. The majority of the non-extractable residues appeared to be due to stable covalent binding to soil organic matter.     

Studies on bound 14C-prometryn residues in soil and plants

A high-temperature distillation technique was developed for determining and chemically identifying the bound (nonextractable) residues of ¹⁴C-prometryn in an organic soil and plants. A considerable portion of the bound ¹⁴C residues in the incubated organic soil was identified as prometryn. These residues were absorbed by plants grown in the soil. Hono-and di-$\text{N}$-dealkylated metabolites of prometryn were present in the plant bound ¹⁴C residues and a major portion of bound residues as associated with lignin. Soil-bound ¹⁴C residues were also released from soil by microbes. The bound ¹⁴C residues in soil were associated with humin, humic acid, and fulvic acid fractions. Thermoanalytical methods were used to obtained information on the nature and location of ¹⁴C bound residues in soil and humic materials.     

Plants' use of different nitrogen forms in response to crude oil contamination

In this study, we investigated Phragmites australis’ use of different forms of nitrogen (N) and associated soil N transformations in response to petroleum contamination. ¹⁵N tracer studies indicated that the total amount of inorganic and organic N assimilated by P. australis was low in petroleum-contaminated soil, while the rates of inorganic and organic N uptake on a per-unit-biomass basis were higher in petroleum-contaminated soil than those in un-contaminated soil. The percentage of organic N in total plant-assimilated N increased with petroleum concentration. In addition, high gross N immobilization and nitrification rates relative to gross N mineralization rate might reduce inorganic-N availability to the plants. Therefore, the enhanced rate of N uptake and increased importance of organic N in plant N assimilation might be of great significance to plants growing in petroleum-contaminated soils. Our results suggest that plants might regulate N capture under petroleum contamination.     

Metabolic fate of the 14C-labeled herbicide clodinafop-propargyl in soil

The metabolic fate of ¹⁴C-phenyl-labeled herbicide clodinafop-propargyl (CfP) was studied for 28 days in lab assays using a soil from Germany (A_p horizon, silt loam, and cambisol). Mineralization amounted to 12.40% of applied ¹⁴C after 28 days showing a distinct lag phase until day 7 of incubation. Portions of radioactivity extractable by means of 0.01 M CaCl₂ solution (bioavailable fraction) decreased rapidly and were 4.41% after 28 days. Even immediately after application, only 57.31% were extracted with the aqueous solvent. Subsequent extraction using accelerated solvent extraction (ASE; acetonitrile/water 4:1, v/v) released 39.91% of applied ¹⁴C with day 0 and 26.16% with day 28 of incubation from the samples. Non-extractable portions of radioactivity thus, increased with time amounting to 11.99% (day 0) and 65.00% (day 28). A remarkable increase was observed between 14 and 28 days correlating with the distinct increase of mineralization. No correlation was found throughout incubation with general microbial activity as determined by DMSO reduction. Analysis of the CaCl₂ and ASE extracts by radio-TLC, radio-HPLC and GC/MS revealed that CfP was rapidly cleaved to free acid clodinafop (Cf), which was further (bio-) transformed; DT₅₀ values (based on radio-TLC detection of the parent compound) were far below 1 day (CfP) and about 7 days (Cf). TLC analysis pointed to 2-(4-hydroxyphenoxy)-propionic acid as further metabolite. Due to fractionation of non-extractable residues, most of the ¹⁴C was associated with fulvic and humic acids, portions in humin fractions and non-humics were moderate and low, respectively. Using a special strategy, which included pre-incubation of the soil with CfP and then mineralization of ¹⁴C-CfP as criterion, a microorganism was isolated from the soil examined. The microorganism grew using CfP as sole carbon source with concomitant evolution of ¹⁴CO₂. The bacterium was characterized by growth on commonly used carbon sources and by 16S rDNA sequence analysis. The sequence exhibited high similarity with that of Rhodococcus wratislaviensis (99.56%; DSM 44107, NCIMB 13082).     

Deltamethrin degradation and effects on soil microbial activity

Deltamethrin [(S)-cyano-3-phenoxybenzyl-cis-(1R,3R)-2,2-dimethyl) cyclo–propane carboxylate),1] labelled at gem-dimethyl groups of the cyclopropane ring was applied on two Egyptian soils at a level of 10 mg/kg soil for a laboratory incubation experiment under aerobic and anaerobic conditions. A steady decrease of soil extractable¹⁴C-residues, accompanied by a corresponding increase of non- extractable bound ¹⁴C-residues was observed over a 90-day incubation period. The percentage of evolved ¹⁴CO₂ increased with time under aerobic and anaerobic conditions in both soils. The effect of deltamethrin on soil microorganisms as well as the counter effect of microorganisms on the insecticide was also investigated. As the incubation period increased, the inhibitory effect of the insecticide on the microorganisms decreased and the evolution of carbon dioxide depended on the applied dose. The nature of soil methanol soluble residues was determined by chromatographic analysis which revealed the presence of the parent insecticide as the main product in addition to four metabolites: 3-(2′,2′-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid (II); 3-phenoxybenzaldehyde (III); 3-phenoxybenzoic acid (IV); 3-phenoxybenzyl alcohol (V).     

Evaluation of the ecotoxicological impact of the organochlorine chlordecone on soil microbial community structure,abundance, and function

The insecticide chlordecone applied for decades in banana plantations currently contaminates 20,000 ha of arable land in the French West Indies. Although the impact of various pesticides on soil microorganisms has been studied, chlordecone toxicity to the soil microbial community has never been assessed. We investigated in two different soils (sandy loam and silty loam) exposed to different concentrations of CLD (D0, control; D1 and D10, 1 and 10 times the agronomical dose) over different periods of time (3, 7, and 32 days): (i) the fate of chlordecone by measuring ¹⁴C-chlordecone mass balance and (ii) the impact of chlordecone on microbial community structure, abundance, and function, using standardized methods (-A-RISA, taxon-specific quantitative PCR (qPCR), and ¹⁴C-compounds mineralizing activity). Mineralization of ¹⁴C-chlordecone was inferior below 1 % of initial ¹⁴C-activity. Less than 2 % of ¹⁴C-activity was retrieved from the water-soluble fraction, while most of it remained in the organic-solvent-extractable fraction (75 % of initial ¹⁴C-activity). Only 23 % of the remaining ¹⁴C-activity was measured in nonextractable fraction. The fate of chlordecone significantly differed between the two soils. The soluble and nonextractable fractions were significantly higher in sandy loam soil than in silty loam soil. All the measured microbiological parameters allowed discriminating statistically the two soils and showed a variation over time. The genetic structure of the bacterial community remained insensitive to chlordecone exposure in silty loam soil. In response to chlordecone exposure, the abundance of Gram-negative bacterial groups (β-, γ-Proteobacteria, Planctomycetes, and Bacteroidetes) was significantly modified only in sandy loam soil. The mineralization of ¹⁴C-sodium acetate and ¹⁴C-2,4-d was insensitive to chlordecone exposure in silty loam soil. However, mineralization of ¹⁴C-sodium acetate was significantly reduced in soil microcosms of sandy loam soil exposed to chlordecone as compared to the control (D0). These data show that chlordecone exposure induced changes in microbial community taxonomic composition and function in one of the two soils, suggesting microbial toxicity of this organochlorine.     

Laboratory studies on volatilization and mineralization of 14c‐p,p'‐DDT in soil,release of bound residues and dissipation from solid surfaces

Abstract

In support of field data, laboratory studies were conducted on volatilization, mineralization and binding of ¹⁴C‐p,p'‐DDT in soils at Sao Paulo. Incubation of soil for 6 weeks did not result in volatilized organics or mineralization; with >95% extractable radiocarbon in the form of p,p'‐DDT. Small amounts of bound residues (1.8%) were detected in soil. These data confirm the very slow dissipation of DDT in the field which presumably relates to the acidic pH of soil (4.5–4.8).

Bound ¹⁴C‐residues in soils treated with ¹⁴C‐p,p'‐DDT at Praia Grande and Sao Paulo could be released (5–21%) by sulphuric acid treatment. The released residue had the composition: 69–90% DDT, 7–32% DDD and 0–3% DDE. Incubation of soil bound ¹⁴C‐residues with fresh inoculum for 3 months did not result in release of ¹⁴C.

Dissipation from wooden surfaces was fairly slow. After 20 weeks, 74% of the applied radioactivity could be recovered; 44% hexane‐non‐extractable.     

Simulation of global warming potential (GWP) from rice fields in the Tai-Lake region,China by coupling 1:50,000 soil database with DNDC model

Quantifying greenhouse gas (GHG) emissions from wetland ecosystems is a relatively new issue in global climate change studies. China has approximately 22% of the world's rice paddies and 38% of the world's rice production, which are crucial to accurately estimate the global warming potential (GWP) at regional scale. This paper reports an application of a biogeochemical model (DeNitrification and DeComposition or DNDC) for quantifying GWP from rice fields in the Tai-Lake region of China. For this application, DNDC is linked to a 1:50,000 soil database, which was derived from 1107 paddy soil profiles compiled during the Second National Soil Survey of China in the 1980–1990s. The simulated results show that the 2.34 Mha of paddy soil cultivated in rice–wheat rotation in the Tai-Lake region emitted about ?1.48 Tg C, 0.84 Tg N and 5.67 Tg C as CO₂, N₂O, and CH₄ respectively, with a cumulative GWP of 565 Tg CO₂ equivalent from 1982 to 2000. As for soil subgroups, the highest GWP (26,900 kg CO₂ equivalent ha^?1 yr^?1) was linked to gleyed paddy soils accounting for about 4.4% of the total area of paddy soils. The lowest GWP (5370 kg CO₂ equivalent ha^?1 yr^?1) was associated with submergenic paddy soils accounting for about 0.32% of the total area of paddy soils. The most common soil in the area was hydromorphic paddy soils, which accounted for about 53% of the total area of paddy soils with a GWP of 12,300 kg CO₂ equivalent ha^?1 yr^?1. On a regional basis, the annual averaged GWP in the polder, Tai-Lake plain, and alluvial plain soil regions was distinctly higher than that in the low mountainous and Hilly soil regions. As for administrative areas, the average annual GWP of counties in Shanghai city was high. Conversely, the average annual GWP of counties in Jiangsu province was low. The high variability in soil properties throughout the Tai-Lake region is important and affects the net greenhouse gas emissions. Therefore, the use of detailed soil data sets with high-resolution digital soil maps is essential to improve the accuracy of GWP estimates with process-based models at regional and national scales.