Pesticides In Agricultural Soils Research Articles

Residues of Organic Chlorinated Pesticides in Agricultural Soils of Beijing, China

Concentration of organic chlorinated pesticides (OCPs) were measured in topsoils of a selected farm (NK farm) in Beijing in 1993 and 2003. The results indicated that OCPs, mainly 1,2,3,4,5,6-hexachlorocyclohexane (HCH) and 1,1,1,-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT), degraded greatly in the 20 years after the prohibition of their use. DDT was the major contributors of pollution on the farm with 92.23% and 81.28% contributions of total OCP load in soils in 2003 and 1993 respectively. The levels of total DDT and HCH in the old orchard group, in which cultivation began in 1962, were significantly higher (p < 0.05) than those in the new orchard group in which cultivation began in 1991, and all data were higher than the level of barren land (p < 0.05). Studying the isomeric and parent substance metabolite ratios indicated there was more application and accumulation of DDT in the old orchard and that DDT in the new orchard had undergone a different degradation time period or perhaps had been applied more recently, but no new input of HCH was detected. Pollution potential was assessed on the basis of China Soil Environmental Quality Standard.

Organochlorine Pesticides in Agricultural Soil and Vegetables from Tianjin, China

Samples of eight types of vegetables, the rhizosphere soils, and bulk soils were collected from two sites (A and B) in Tianjin, China for the determination of hexachlorocyclohexane isomers (HCHs) and dichlorodiphenyltrichloroethane and metabolites (DDXs). The average concentrations of total HCHs and DDXs in the bulk soils were 3.6 and 80.1 ng/g for site A and 102 and 235 ng/g for site B, respectively. Relative accumulations of HCHs and DDXs in the rhizosphere soil from site A but not site B were demonstrated. The concentrations of total HCHs and DDXs in vegetable roots were 3.6-60 and 4.2-73 ng/g for site A and 15-152 and 7.1-136 ng/g for site B, respectively. Difference in bioaccumulation among various vegetables, especially between tuber and fibrous vegetables was significant. DDXs in spinach and cauliflower from site B and lindane (gamma-HCH) in cauliflower from both sites and violet from site B exceeded the maximum residual limits. Linear correlation of log-transformed HCHs and DDXs contents between the vegetable roots and the rhizosphere soils suggests the direct uptake of HCHs and DDXs.

Influence of pH on pesticide sorption by soil containing wheat residue-derived char

Field burning of crop residues incorporates resulting chars into soil and may thus influence the environmental fate of pesticides in the soil. This study evaluated the influence of pH on the sorption of diuron, bromoxynil, and ametryne by a soil in the presence and absence of a wheat residue-derived char. The sorption was measured at pHs ∼3.0 and ∼7.0. Wheat char was found to be a highly effective sorbent for the pesticides, and its presence (1% by weight) in soil contributed >70% to the pesticide sorption (with one exception). The sorption of diuron was not influenced by pH, due to its electroneutrality. Bromoxynil becomes dissociated at high pHs to form anionic species. Its sorption by soil and wheat char was lower at pH ∼7.0 than at pH ∼3.0, probably due to reduced partition of the anionic species of bromoxynil into soil organic matter and its weak interaction with the carbon surface of the char. Ametryne in its molecular form at pH ∼7.0 was sorbed by char-amended soil via partitioning into soil organic matter and interaction with the carbon surface of the char. Protonated ametryne at pH ∼3.0 was substantially sorbed by soil primarily via electrostatic forces. Sorption of protonated ametryne by wheat char was also significant, likely due not only to the interaction with the carbon surface but also to interactions with hydrated silica and surface functional groups of the char. Sorption of ametryne by char-amended soil at pH ∼3.0 was thus influenced by both the soil and the char. Environmental conditions may thus significantly influence the sorption and behavior of pesticides in agricultural soils containing crop residue-derived chars.

Reduced Biodegradation of Benzonitrile in Soil Containing Wheat‐Residue‐Derived Ash

Burning of crop residues is a common agricultural practice that incorporates the resulting particulate matter (ash) of high adsorptivity into soils. To investigate the effect of ash on the biodegradation of pesticides in soils, we measured the sorption, desorption, and biodegradation of benzonitrile in a silt loam in the presence and absence of an ash resulting from burning of wheat (Triticum aestivum L.) residue. Biodegradation experiments were conducted by inoculating sorbent slurries with a pure culture of benzonitrile-degrading bacteria (Nocardia sp.). Both liquid- and sorbed-phase benzonitrile concentrations were quantified over time. The ash was approximately 2000 times more effective per unit mass than the soil in sorbing benzonitrile. Amendment of the soil with 1% ash (by weight) resulted in a 10-fold increase in sorption. Sorption of benzonitrile by the ash significantly decreased the solution-phase concentration in the slurries of ash and ash-amended soil. Desorption of benzonitrile from the ash required approximately 60 min to complete, whereas approximately 20 min were required for desorption from the soil. Benzonitrile in the extracts of various sorbents and soil slurry was completely degraded within 500 min. However, the degradation was substantially reduced in the presence of the ash. At 2000 min, only 20% of benzonitrile in ash slurry and only 44% in ash-amended soil slurry were degraded. An acclimation period of approximately 100 min was observed in extracts and slurries containing the ash. Substantial reduction in the biodegradation of benzonitrile in the presence of wheat ash was apparently due to sorption of benzonitrile by the ash, slow desorption from the ash, and the increased acclimation period. Our results suggest that the presence of crop-residue-derived ash may increase the persistence of pesticides in agricultural soils.

Pesticide adsorptivity of aged particulate matter arising from crop residue burns.

Particulates (ashes) arising from the burning of crop residues are potentially effective adsorbents for pesticides in agricultural soils. To determine the long-term adsorptive sustainability of ashes, a wheat (Triticum aestivum L.) ash was aged under environmentally relevant conditions (in CaCl(2) solution at room temperature and pH 7) in soil extract for 1 month and in a soil (1% ash) for a period of up to 12 months. The aged ash and ash-amended soil were used to sorb diuron from water. The diuron sorption was also measured in the presence of atrazine as a competing pesticide. There was no observed microbial impact on the stability of the wheat ash in soil. All isotherms with the ash were nonlinear type-I curves, suggestive of the surface adsorption. On a unit mass basis, the ash in soil extract was 600-10000 times more effective than the soil in sorbing diuron. Adsorption of dissolved soil organic matter (DOM) during aging on the ash surfaces reduced the diuron adsorption by 50-60%. Surface competition from the atrazine adsorption also reduced the ash adsorption of diuron by 10-30%. A total of 55-67% reduction in diuron sorption by the ash-amended soil was observed. Due to its high initial adsorptivity, the ash fraction of the aged ash-amended soil contributed >50% to the total diuron sorption. Thus, the wheat ash aged in the soil remained highly effective in adsorbing diuron. As crop residues are frequently burned in the field, pesticides in agricultural soils may be highly immobilized due to the presence of ashes.

Air−Soil Exchange of Organochlorine Pesticides in Agricultural Soils. 1. Field Measurements Using a Novel in Situ Sampling Device

Initial results are presented for in situ measurements of soil−air partitioning for a range of organochlorine (OC) pesticides in two contaminated agricultural soils. A soil survey was conducted and used to identify high levels of several OC pesticides in two regions of southern Ontario that are known for their intensive agriculture, the Tobacco Belt and the Holland Marsh. Experiments were conducted at one field in each region by sampling air very close to the soil surface using a disc-shaped sampler. The equilibrium status of the sampled air was tested by comparing the chiral signature of the soil with the signature in air sampled by the device and ambient air. Although results showed that 104% of trans-chlordane (TC) and 96% of cis-chlordane (CC) in the air under the sampler originated from the soil, the propagated errors in these results (34% SD for TC and 26% SD for CC) are too large to provide conclusive evidence for equilibrium. Therefore, a soil−air quotient (QSA) is reported here instead of the soil−air partition coefficient (KSA). This value is an approximation of the “true” KSA. Results show a linear relationship between log QSA and log KOA and fit in with the relationship KSA = 0.411ρφOCKOA where ρ is the soil density (kg L-1). Using this relationship, fugacities were calculated in air and soil. Results of this calculation identify a strong disparity that favors soil-to-air transfer. This gradient is confirmed by measurements at different heights over one of the fields. Soil−air exchange is a key process in the overall fate of OC pesticides. The results from this study will improve our ability to model this process and account for differences between soils.

Determination of organochlorine pesticides in agricultural soil with special reference to gamma-HCH degradation by Pseudomonas strains.

Soil samples were taken from different agricultural fields and analyzed for organochlorine pesticide residues by gas chromatography. The analysis indicated that the soil samples contained some common organochlorine pesticides DDT, DDD, DDE, HCH and Aldrin. gamma-HCH was detected as 47.35 ppb whereas the concentrations of alpha-HCH, beta-HCH, p('),p(')-DDE, o('),p(')-DDT were 38.81, 1.79, 7.10 and 13.30 ppb, respectively, in the same soil. Two Pseudomonas strains isolated from agricultural soil were found to possess gamma-hexachlorocyclohexane degrading ability when the isolates were grown in a mineral salt medium containing gamma-HCH as the sole source of carbon and a number of metabolites were produced and detected by the gas chromatography. These bacterial isolates were further tested for carbohydrate and amino acid utilization as well as for their susceptibility against 10 commonly used antibiotics namely amoxycillin, chloramphenicol, cloxacillin, doxycycline, methicillin, nalidixic acid, neomycin, nitrofurantoin, streptomycin and tetracycline. Both the isolates were also screened for plasmid DNA and found to harbour a single plasmid.

Transformation and binding of 13C and 14C‐labelled atrazine in relation to straw decomposition in soil

SummaryAs a source of organic matter, crop residues affect the behaviour of pesticides in agricultural soils. The fate of [U‐ring‐13C] and [U‐ring‐14C] atrazine (6‐chloro‐N‐ethyl‐N‐isopropyl‐1,3,5‐triazine‐2,4‐diamine) was investigated during laboratory incubation under controlled conditions in a loamy soil amended with wheat straw at two different states of decomposition: no preliminary decomposition or 6 months’ preliminary decomposition. After 3 months, non‐extractable, so‐called ‘bound’, 13C‐atrazine residues were recovered in three particle‐size fractions (&gt; 200, 50–200 and &lt; 50 μm), and investigated with solid‐state 13C‐NMR spectroscopy. Parallel incubations with [U‐ring‐14C] atrazine were carried out to quantify the bound residues as well as the extractable and mineralized fractions. The effect of straw residues on atrazine behaviour depended on whether they had been previously decomposed or not. When straw was decomposed for 6 months prior to incubation, atrazine mineralization was enhanced to 50% of the initial 14C in contrast to 15% of the initial 14C in soil alone and soil amended with fresh straw. In parallel, atrazine bound residues were formed in greater amount representing up to 20% of the initial 14C. CP/MAS 13C‐NMR on soil size fractions of soil–straw mixtures after incubation with 13C‐atrazine showed that bound residues contained mostly triazinic C, corresponding to atrazine or primary metabolites. Non‐humified organic materials recovered in size fractions &gt; 200 and 50–200 μm contained significant amounts of bound residues, especially when straw was added to the soil. CP/MAS 13C‐NMR analysis of humic acids obtained from &lt; 50‐μm fractions was difficult due to overlapping of the native carboxyl 13C signal with the 13C‐atrazine signal.

Use of lysimeters to estimate leaching of pesticides in agricultural soils

In this review of lysimeters, different aspects concerning soil-filling technique, lysimeter size and materials, and drainage-system type are discussed. The placement of lysimeters in the field is dealt with, as are other types of field measurements that can provide complementary information. Evaluations of various properties are based on the assumption that the lysimeters are to be used for estimating pesticide leaching. Guidelines for use in designing a suitable lysimeter experiment for this purpose are described, with special emphasis placed on using the results as a basis for pesticide registration. In this context, some general recommendations are identified. Concerning the lysimeter itself, stress is placed on the importance of using undisturbed soil monoliths. It is recommended that two soil types, i.e. sand and clay, be used and that the management practices carried out closely resemble normal farming practices. Further recommendations include weekly water sampling, two watering regimes, and use of the normal and double the normal application rate of pesticides.