The effect of landuse on soil organic carbon chemistry and sorption of pesticides and metabolites

Earlier studies had shown significant differences in sorption of nine pesticides in soils collected from two landuses (native vegetation and market gardens), which could not be explained on the basis of organic carbon content alone. Consequently it was hypothesised that the differences in sorption behaviour between the two landuses may be due to variation in the chemistry of the organic carbon. In this study the relationship between sorption behaviour of the nine chemicals and soil organic carbon chemistry, as determined by solid-state (13)C NMR spectroscopy, was investigated. No significant differences were found between the two landuses in the distribution of the four main spectral regions of the (13)C NMR spectra of soil OC, except for the carbonyl fraction (165-220ppm), which may reflect the low OC content of the soils from both landuses. For all chemicals, except prometryne, the most significant (P<0.01 or P<0.001) relationship between K(d) values and types of OC was found with the aromatic (110-165ppm) or the alkyl (0-45ppm) fraction. A comparison was made of the variability of K(d) values normalized over OC (i.e. K(oc)), alkyl, aromatic and alkyl+aromatic fractions. Expressing K(d) values for all chemicals, except azinphos methyl, in soils under native vegetation as K(alkyl) or K(aromatic) greatly decreased the variability compared with the K(oc) value. However in the cultivated soils only the sorption coefficients for DEA, DIA and fenamiphos showed a decrease in variability when expressed as K(alkyl) or K(aromatic). This reflected the stronger relationship between sorption coefficients and the alkyl and aromatic fraction of soil OC in soils from native vegetation compared with those determined from the market garden soils. The different relationships between sorption coefficients and types of OC of the two landuses also suggests that the type of aromatic and alkyl carbon under the two landuses is different and NMR characterisation of the OC was not sufficient to distinguish these differences.     

Simultaneous analysis of triasulfuron, metsulfuron-methyl and chlorsulfuron in water and alkaline soils by high-performance liquid chromatography

A method capable of simultaneously detecting residues of three sulfonylurea herbicides at microgram/l and microgram/kg level in water and alkaline soils has been described. The method is based on solid phase extraction and HPLC with UV detection. In alkaline soils especially those containing low organic carbon it was possible to extract the herbicides with de-ionised water and no clean up step was needed. Soil samples spiked with technical grade triasulfuron, metsulfuron-methyl and chlorsulfuron were extracted twice by shaking with de-ionised water for one hour and centrifuging at 10,000 rpm for 15 minutes. Supernatants filtered through glass micro-fibre filters were passed through C18 cartridges previously pre-conditioned with methanol and de-ionised water at a flow rate of < 20 ml/min. Residues of the herbicides retained on the cartridge were eluted with acidified methanol. The eluate was analysed by HPLC. A C18 column was used with a mobile phase of methanol/water (40 + 60, V/V for for the herbicide residues were 1.0 microgram/l and 3 micrograms/kg in water and soil, respectively. The average recoveries for water samples ranged from 73-94%, while for soil samples recoveries were 77-97% for the three compounds studied.     

Rapid multiresidue determination for currently used pesticides in agricultural drainage waters and soils using gas chromatography–mass spectrometry

An efficient and sensitive method for simultaneous determination of 38 pesticides in agricultural drainage waters and soils has been developed and validated. Water samples were extracted using solid-phase extraction with C18 cartridges while solid samples (suspended particle matter and soil) were extracted by using the quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction method. The target pesticides were analyzed by using gas chromatography-mass spectrometry with electron impact ionization. The proposed method allowed a simultaneous determination and confirmation of a large number of pesticides in agricultural drainage waters, suspended particle matters and soils/sediments with a good reproducibility and low detection limits. The developed method was applied to a survey of pesticides in a vegetable growing area of Guangzhou, China. The pesticides commonly found in the area were butachlor, carbofuran, dichlorvos, fipronil, isocarbophos and pyridaben.     

Impact of climatic and soil conditions on environmental fate of atrazine used under plantation forestry in Australia

We studied the leaching and dissipation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-s-triazine) and its two principal metabolites (desethylatrazine and desisopropylatrazine) for more than two years through soil profiles at five forestry sites across Australia (representing subtropical, temperate and Mediterranean climatic conditions with rainfall ranging from 780 to 1536 mm yr^?1). Following atrazine applications at local label rates, soil cores were collected at regular intervals (up to depths of 90–150 cm), and the residues of the three compounds in soil were analysed in composite samples using liquid chromatography. Bromide was applied simultaneously with atrazine to follow the movement of the soil water. While bromide ion rapidly leached through the entire profile, in most cases the bulk of atrazine, desethylatrazine and desisopropylatrazine remained in the top 45 cm of the soil profile. However, a small fraction of residue moved deeper into the soil profile and at a subtropical site (Toolara) trace levels (ng L^?1) of atrazine and one of its metabolites (DEA) were detected in perched groundwater located at a depth of 1.8 m. Data on the total residues of atrazine in soil profiles from all sites except the Tasmanian site fitted a first-order decay model. The half-life of atrazine in surface soils at the subtropical sites (Toolara and Imbil) ranged from 11 to 21 days. Four separate applications of atrazine at Toolara resulted in a narrow range of half-lives (16 ± 3.6 days), confirming relatively rapid dissipation of atrazine under subtropical conditions (Queensland). In contrast, a prominent biphasic pattern of initial rapid loss followed by very slow phase of degradation of atrazine was observed under the colder temperate climate of Highclere (Tasmania). The data showed that while its 50% (DT₅₀) loss occurred relatively rapidly (36 days), more than 10% of herbicide residue was still detectable in the profile even a year after application (DT₉₀ = 375 days). The rate of dissipation of atrazine at warm subtropical Queensland sites (Imbil and Toolara) was 2–3 times faster than sites located in colder climate of Tasmania. The marked contrast in DT₅₀ values between subtropical and temperate sites suggest that climatic conditions (soil temperature) is one of the key factors affecting atrazine dissipation. At the Tasmanian site, the combination of leaching of the herbicide in subsoil and slower microbial activity at cooler temperatures would have caused a longer persistence of atrazine.     

Effects of thiobencarb in combinations with molinate and chlorpyrifos on selected soil microbial processes

The impact of pesticides, namely thiobencarb (TBC), molinate (MOL) and chlorpyrifos (CPF), on soil microbial processes was studied in two Australian soils. Substrate induced respiration (SIR), substrate induced nitrification (SIN) and phosphatases and chitinase enzymatic activities were assessed during a 30-day microcosm study. The pesticides were applied to soils at recommended rates either alone, or as binary mixtures with TBC. Soil samples were sampled at 5, 15 and 30 days after pesticide treatments. Substrate induced respiration was only transiently affected by pesticides in both soils. In contrast, the process of indigenous nitrification was affected by the presence of pesticides in both soils, especially when the pesticides were applied as binary mixtures. Substrate induced nitrification increased with pesticides in the Griffith soil (except with MOL+TBC after 5 days) whereas SIN values were non-significantly different to the control on the Coleambally soil. The binary mixtures of pesticides with TBC resulted in a decrease in SIN in both soils, but the effects disappeared within 30 days. The enzymatic activities were not consistently affected by pesticides, and varied with the soil and pesticides studied. This study showed that, when applied at recommended application rates, TBC, MOL, and CPF (individually or as binary mixtures), had little or only transitory effects on the functional endpoints studied. However, further investigations are needed to assess the effect on microbial densities and community structure despite the low disturbance to the functions noted in this work.     

Cadmium adsorption and desorption behaviour on goethite at low equilibrium concentrations: effects of pH and index cations

The transport and bioavailability of cadmium is governed mainly by its adsorption-desorption reactions with minerals such as goethite--a common iron oxide mineral in variable charged and highly weathered tropical soils. Soil factors such as pH, temperature, solution Cd concentration, ionic strength and ageing affect Cd adsorption on goethite. The desorption behaviour of Cd from goethite at low concentrations is not fully understood. This study investigates the adsorption-desorption of Cd at low Cd concentrations (Cd adsorbed on goethite from 20 to 300 microM Cd solutions) in Na and Ca nitrate solutions of 0.03 M nominal ionic strengths. Synthetic goethite prepared by ageing a ferric hydroxide gel at high pH and room temperature was used for Cd adsorption and desorption studies. For desorption experiment 10 successive desorptions were made for the whole range of initial Cd concentrations (20-300 microM) in the presence of 0.01 M Ca(NO3)2 or 0.03 M NaNO3 solutions. Cadmium adsorption was found to be higher in Na+ than Ca2+ probably due to the competition of Ca2+ ions with Cd2+ ions for adsorption sites on the surfaces of goethite. The effect of index cation on Cd adsorption diminished with increase in pH from 5.0 to 6.0. Cadmium desorption decreased with increase in pH from 5.0 to 6.0 in both Na and Ca systems. After 10 successive desorptions with 0.03 M NaNO3 at the lowest initially adsorbed Cd approximately 45%, 20% and 7% of the adsorbed Cd was desorbed at pH 5.0, 5.5 and 6.0, respectively. The corresponding desorptions in the presence of 0.01 M Ca(NO3)2 were 49%, 22% and 8%, respectively. The Freundlich parameter, k, based on each progressive step of desorption at different adsorbed concentration increased with increasing desorption step, which may indicates that a fraction of Cd was resistant to desorption. Low Cd desorbability from goethite may be due to its specific adsorption and/or possibly as a result of Cd entrapment in the cracks or defects in goethite structure.     

The distribution of triclosan and methyl-triclosan in marine sediments of Barker Inlet, South Australia

In this work, we investigated the transport and burial of triclosan and its methylated derivative, in surface sediments near the mouth of Barker Inlet in South Australia. The most likely source of this commonly used bactericide to the area is a wastewater outfall discharging at the confluence of the inlet with marine waters. Triclosan was detected in all samples, at concentrations (5-27 μg kg(-1)) comparable to values found in other surface sediments under the influence of marine wastewater outfalls. Its dispersal was closely associated with fine and organic-rich fractions of the sediments. Methyl-triclosan was detected in approximately half of the samples at concentrations <11 μg kg(-1). The occurrence of this compound was linked to both wastewater discharges and biological methylation of the parent compound. Wastewater-borne methyl-triclosan had a smaller spatial footprint than triclosan and was mostly deposited in close proximity to the outfall. In situ methylation of triclosan likely occurs at deeper depositional sites, whereas the absence of methyl-triclosan from shallower sediments was potentially explained by photodegradation of the parent compound. Based on partition equilibrium, a concentration of triclosan in the order of 1 μg L(-1) was estimated in sediment porewaters, a value lower than the threshold reported for harmful effects to occur in the couple of species of marine phytoplankton investigated to date. Methyl-triclosan presents a greater potential for bioaccumulation than triclosan, but the implications of its occurrence to aquatic ecosystem health are difficult to predict given the lack of ecotoxicological data in the current literature.     

Dissipation of sulfamethoxazole and trimethoprim antibiotics from manure-amended soils

In this study, the dissipation of two antibiotics, sulfamethoxazole (SMX) and trimethoprim (TRM), in three soils under both aerobic and anaerobic conditions are evaluated. Under aerobic conditions, SMX dissipated rapidly through biodegradation but TRM was more persistent. Within the first 20 days in biologically active soils, >50% of the SMX was lost from the clay loam and loamy sand soils, and >80% loss was noted in the loam soil. Anaerobic dissipation of both compounds was more rapid than aerobic dissipation. The addition of manure to the soil only slightly increased the initial dissipation rate of the two compounds. Little effect was found on glucose mineralisation in soil following the addition of SMX and TRM, even as mixtures at high concentrations.     

On-line solid-phase extraction and fluorescence detection of selected endocrine disrupting chemicals in water by high-performance liquid chromatography

A high-performance liquid chromatographic method was developed to analyse selected endocrine disrupting chemicals in water by using automated on-line solid-phase extraction with a fluorescence detector. The excitation and emission wavelengths of the fluorescence detector were 230 nm and 290 nm, respectively. The selected endocrine disrupting chemicals include hormone steroids such as estradiol (E2), estriol (E3), ethynylestradiol (EE2), and ethynylestradiol 3-methyl ether (MeEE2) as well as nonylphenols (NP), octylphenols (OP), POE(1-2) nonyl phenol (NPE) and bisphenol A (BP). Three types of on-line cartridges (C18, PLRP-s and PRP-1) were tested to pre-concentrate the endocrine disruptors in deionised water. It was found that the recoveries of these chemicals at 1 microg/L were close to 100% except for 4-octyl phenol and 4-n-nonyl phenol, which had recoveries of about 40% to 80%. The two polymer cartridges (PLRP-s and PRP-1) gave higher recoveries than the C18 cartridges. The addition of methanol at 5% to 10% in water significantly improved the recovery of 4-octyl phenol and 4-n-nonyl phenol. The addition of methanol also led to an improvement in the recovery with C18 cartridges. With the addition of methanol in water samples, these three types of cartridges gave similar recoveries for the chemicals. The detection limits of this method ranged from 20 ng/L to 50 ng/L. A river water sample spiked with these chemicals was analysed using the above method and we found no interference with the peaks of the selected endocrine disrupting chemicals. The recoveries for these chemicals were more than 92% except for 4-NP with a recovery of 61%. This relatively simple method is useful for laboratory studies on the environmental fate of these endocrine disrupting chemicals in water.     

Sorption of fipronil and its metabolites on soils from South Australia

This paper reports on the sorption of fipronil [(+/-)-5-amino-1-(2,6-dichloro-alpha,alpha,alpha-trifluoro-p-tolyl)-4-trifluoromethyl-sulfinylpyrazole-3-carbonitrile] and its two main metabolites, desulfynil and sulfide derivatives on a range of soils from South Australia. The Freundlich sorption coefficient (Kf) values for fipronil on the soils ranged from 1.94 to 4.84 using a 5% acetonitrile/water mixture as the soil solution. Its two metabolites had a higher sorption affinity for soils, with Kf values ranging from 11.09 to 23.49 for the sulfide derivative and from 4.70 to 11.77 for the desulfynil derivative. Their sorption coefficients were found to be better related to the soil organic carbon than clay content. The presence of cosolvents in soil solutions had a significant influence on the sorption of fipronil. The Freundlich sorption coefficients showed a log linear relationship with the fractions of both acetonitrile and methanol in solutions. The sorption coefficient of fipronil on Turretfield soil in the aqueous solution was estimated to be from 13.80 to 19.19. Methanol had less effect on the sorption of fipronil than acetonitrile. The Kd values for fipronil on the eight soils using a 5% methanol/water mixture were from 5.34 to 13.85, which reflect more closely the sorption in the aqueous solution. The average Koc value for fipronil on the eight South Australian soils was calculated to be 825+/-214.