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This study investigated the mobilization of a wide range of per- and polyfluoroalkyl substances (PFASs) present in aqueous film-forming foams (AFFFs) in water-saturated soils through one-dimensional (1-D) column experiments with a view to assessing the feasibility of their remediation by soil desorption and washing. Results indicated that sorption/desorption of most of the shorter-carbon-chain PFASs (C≤ 6) in soil reached greater than 99% rapidly─after approximately two pore volumes (PVs) and were well predicted by an equilibrium transport model, indicating that they will be readily removed by soil washing technologies. In contrast, the equilibrium model failed to predict the mobilization of longer-chain PFASs (C≥ 7), indicating the presence of nonequilibrium sorption/desorption (confirmed by a flow interruption experiment). The actual time taken to attain 99% sorption/desorption was up to 5 times longer than predicted by the equilibrium model (e.g., ∼62 PVs versus ∼12 PVs predicted for perfluorooctane sulfonate (PFOS) in loamy sand). The increasing contribution of hydrophobic interactions over the electrostatic interactions is suggested as the main driving factor of the nonequilibrium processes. The inverse linear relationship (R2= 0.6, p< 0.0001) between the nonequilibrium mass transfer rate coefficient and the Freundlich sorption coefficient could potentially be a useful means for preliminary evaluation of potential nonequilibrium sorption/desorption of PFASs in soils.

Soil contaminated with aqueous film-forming foams (AFFFs) containing per- and polyfluoroalkyl substances (PFASs) at firefighting training sites has become a major concern worldwide. To date, most studies have focused on assessing soil–water partitioning behavior of PFASs and the key factors that can affect their sorption, whereas PFASs leaching from contaminated soils have not yet been widely investigated. This study evaluated the leaching and desorption of a wide range of PFASs from twelve contaminated soils using the Australian Standard Leaching Procedure (ASLP), the U.S. EPA Multiple Extraction Procedure (MEP), and Leaching Environmental Assessment Framework (LEAF). All three leaching tests provided a similar assessment of PFAS leaching behavior. Leaching of PFASs from soils was related to C-chain lengths and their functional head groups. While short-chain (CF2≤ 6) PFASs were easily desorbed and leached, long-chain PFASs were more difficult to desorb. PFASs with a carboxylate head group were leached more readily and to a greater extent than those with a sulfonate or sulfonamide head group. Leaching of long-chain PFASs was pH-dependent where leaching increased at high pH, while leaching of short-chain PFASs was less sensitive to pH. Comparing different leaching tests showed that the results using the alkaline ASLP were similar to the cumulative MEP data and the former might be more practical for routine use than the MEP. No single soil property was adequately able to describe PFAS leaching from the soils. Overall, the PFAS chemical structure appeared to have a greater effect on PFAS leaching from soil than soil physicochemical properties.

Nanotechnology may be used to design more performant copper agrochemicals. Assessing the benefits and risks of the novel nano-products requires a good understanding of their fate in soil relative to other forms of copper. This study compares nine forms of Cu including nano and conventional Cu-based formulations, as well as their salt or bulk equivalents. Readily available Cu was extracted with 0.01 M CaCl2over a period of 29 days in three soils with contrasting properties. For eight out of nine formulations, available Cu decreased over time indicating that complexation of Cu with soil phases was the process determining the availability of Cu. Freshly suspended CuO nanoparticles were the only form where available Cu increased over time, indicating that dissolution was limiting availability. The complexation/dissolution kinetics were mainly determined by the soil pH, whereas both soil pH and OC% determined the equilibrium concentration of Cu in the soil solution, in line with results from equilibrium modelling. Overall, the fraction of readily available Cu was very low in all cases, reaching <1% of the Cu added within a couple of weeks. Our results also show that the soil moisture content at the time of Cu amendment can greatly affect the measured available Cu. According to the Cu formulation, amending dry soil resulted in up to 100% more readily available Cu than amending wet soil (pre-incubated at 50% of its maximum water holding capacity for two weeks). Overall, we show that different Cu formulations and soil pre-incubation regime can significantly impact the short term availability of Cu, which is essential to consider when conducting impact or efficacy assessments of (nano)agrochemicals.

Poly- and perfluoroalkyl substances (PFAS) have been widely used worldwide over the last seven decades in >200 diverse industrial applications. Thousands of different PFAS have been used in a wide range of products, such as food packaging, water-repellent and stain-resistant clothing and fire-fighting foams. Partially due to their extreme stability and high mobility, PFAS are now ubiquitous in the environment. Due to their prolonged persistence, some PFAS have been added to the list of persistent organic pollutants. Sorption is one of the fundamental processes that governs environmental fate and effects of organic chemicals. In recent years, a significant body of literature has been published on sorption of PFAS in soils. However, there are conflicting reports about the soil or sediment properties that may be used to predict the mobility of PFAS in the soil environment. This is not surprising because PFAS have complex chemical properties (anionic, cationic and zwitterionic charges together with surface active properties) that influence their sorption–desorption behaviour. Additionally, PFAS show a fluid–water interfacial adsorption phenomenon and such interfaces offer additional retention mechanisms in unsaturated or oil-contaminated soils. In this review, we analyse the literature on sorption and desorption of PFAS to evaluate the dominant soil and solution properties that govern their sorption–desorption behaviour in saturated and unsaturated soils. We also identify the knowledge gaps that need to be addressed in order to gain a sound understanding of their sorption–desorption behaviour in saturated as well as unsaturated soils.

Nanopesticides are not only in an advanced state of research and development but have started to appear on the market. Industry and regulatory agencies need a consolidated and comprehensive framework and guidance for human health risk assessments. In this perspective we develop such a comprehensive framework by exploring two case studies from relevant product types: an active ingredient delivered with a nanocarrier system, and a nanoparticle as an active ingredient. For a nanocarrier system, three entities are tracked during the assessment: the nanocarrier–active ingredient complex, the empty nanocarrier remaining after the complete release of the active ingredient, and the released active ingredient. For the nanoparticle of pure active ingredient, only two entities are relevant: the nanoparticle and the released ions. We suggest important adaptations of the existing pesticide framework to determine the relevant nanopesticide entities and their concentrations for toxicity testing. Depending on the nature of the nanopesticides, additional data requirements, such as those pertaining to durability in biological media and potential for crossing biological barriers, have also been identified. Overall, our framework suggests a tiered approach for human health risk assessment, which is applicable for a range of nanopesticide products to support regulators and industry in making informed decisions on nanopesticide submissions. Brief summaries of suitable methods including references to existing standards (if available) have been included together with an analysis of current knowledge gaps. Our study is an important step towards a harmonized approach accepted by regulatory agencies for assessing nanopesticides.

The aim of this study was to assess the soil–water partitioning behavior of a wider range of per- and polyfluoroalkyl substances (PFASs) onto soils covering diverse soil properties. The PFASs studied include perfluoroalkyl carboxylates (PFCAs), perfluoroalkane sulfonates (PFSAs), fluorotelomer sulfonates (FTSs), nonionic perfluoroalkane sulfonamides (FASAs), cyclic PFAS (PFEtCHxS), per- and polyfluoroalkyl ether acids (GenX, ADONA, 9Cl-PF3ONS), and three aqueous film-forming foam (AFFF)-related zwitterionic PFASs (AmPr-FHxSA, TAmPr-FHxSA, 6:2 FTSA-PrB). Soil–water partitioning coefficients (log Kdvalues) of the PFASs ranged from less than zero to approximately three, were chain-length-dependent, and were significantly linearly related to molecular weight (MW) for PFASs with MW > 350 g/mol (R2= 0.94, p< 0.0001). Across all soils, the Kdvalues of all short-chain PFASs (≤5 −CF2– moieties) were similar and varied less (<0.5 log units) compared to long-chain PFASs (>0.5 to 1.5  log units) and zwitterions AmPr- and TAmPr-FHxSA (∼1.5 to 2 log units). Multiple soil properties described sorption of PFASs better than any single property. The effects of soil properties on sorption were different for anionic, nonionic, and zwitterionic PFASs. Solution pH could change both PFAS speciation and soil chemistry affecting surface complexation and electrostatic processes. The Kdvalues of all PFASs increased when solution pH decreased from approximately eight to three. Short-chain PFASs were less sensitive to solution pH than long-chain PFASs. The results indicate the complex interactions of PFASs with soil surfaces and the need to consider both PFAS type and soil properties to describe mobility in the environment.

Environmental contextThere are great concerns around current wide usage of copper-based agrochemicals. We compare the fate of nano- and conventional forms of copper, in particular their resistance to wash-off by rain (rainfastness), following their application to citrus leaves. Results showing large differences between the formulations in the amount and forms of copper washed from the leaves provide essential information to optimise agrochemical efficacy while minimising the environmental impact. AbstractThis study compares the rainfastness of nine forms of Cu, including nano and conventional Cu-based fungicide formulations, as well as their salt or bulk equivalents. Rainfastness is the ability to resist wash-off; it is a key property for improving pesticide formulations and for assessing the potential transfer of pesticides to the soil. A new protocol was developed to characterise losses of Cu from treated leaves. It consisted of dipping the leaves in rainwater and then in an acid/ethanol mixture followed by size fractionation. The proportion of Cu lost by wash-off from citrus leaves ranged from <2% (Tribasic, nCuO or Cu(OH)2) up to 93% (CuSO4) of the initial amount of Cu applied. Intermediate Cu losses were observed for formulations with silica (nano)particles (9–14% of applied Cu), Kocide (22%), ChampDP (31%), and a formulation with graphene oxide (47%). Smaller particles generally resulted in less wash-off, possibly due to stronger attachment to the leaf surface, but other factors such as the particle shape and solubility also played an essential role. The retention of nCuO to the leaves was particularly high, and the exact mechanisms involved (e.g. foliar uptake) deserve further work. Most of the Cu was washed off in its ionic form (>74%). Two Cu formulations (one commercial formulation and the formulation with graphene oxide) also showed wash off in significant proportions of Cu (~17%) in the nano-sized fraction. This study provides essential information on the amounts and forms of Cu that may reach the soil after the application of Cu-based agrochemicals. The great diversity in behaviour across the range of formulations considered highlights the need for more systematic research to fully exploit the potential improvements of current agrochemicals through (nano)formulation technologies.

Plant protection products containing nanomaterials that alter the functionality or risk profile of active ingredients (nano-enabled pesticides) promise many benefits over conventional pesticide products. These benefits may include improved formulation characteristics, easier application, better targeting of pest species, increased efficacy, lower application rates, and enhanced environmental safety. After many years of research and development, nano-enabled pesticides are starting to make their way into the market. The introduction of this technology raises a number of issues for regulators, including how does the ecological risk assessment of nano-enabled pesticide products differ from that of conventional plant protection products? In this paper, a group drawn from regulatory agencies, academia, research, and the agrochemicals industry offers a perspective on relevant considerations pertaining to the problem formulation phase of the ecological risk assessment of nano-enabled pesticides.

The abiotic protection of low molecular weight organic compounds (LMWOC) in soils may be an important regulator of C cycling. The study of the protection of LMWOC through sorption typically employs soils shaken in solution, which may be compromised by biological activity. We used 14C-labelled glucose as a LMWOC in batch assays of four different soils with contrasting physico-chemical properties (Arenosol, Luvisol, Ferralsol and Andisol). The commonly used biocides NaN3 and HgCl2 were employed alone or in concert across a range of concentrations to assess their efficacy in inhibiting microbial degradation. For short (<1 day) sorption experiments, low NaN3 concentrations (50µM) were sufficient to inhibit microbial activity, whereas for longer (2 week) equilibrium assays, only high HgCl2 concentrations (10mM) were effective in all soils tested. All combinations of biocide were most effective in inhibiting microbial activity in the Arenosol and least effective in the Andisol. Thus, in some soils, particular care is required with biocide selection for complete inhibition of biological activity. The findings presented here are of relevance for the design of studies investigating sorption of labile organic compounds in soils.

The application of biochar technology for soil amendment is largely based on evidence about soil fertility and crop productivity gains made in the Amazonian Black Earth (terra preta). However, the uncertainty of production gains at realistic application rates of biochars and lack of knowledge about other benefits and other concerns may have resulted in poor uptake of biochar technology in Australia so far. In this review, we identify important opportunities as well as challenges in the adoption of biochar technology for broadacre farming and other sectors in Australia. The paper highlights that for biochar technology to be cost-effective and successful, we need to look beyond carbon sequestration and explore other opportunities to value-add to biochar. Therefore, some emerging and novel applications of biochar are identified. We also suggest some priority research areas that need immediate attention in order to realise the full potential of biochar technology in agriculture and other sectors in Australia.

Environmental context Antarctica has several scientific research stations located along its coast, where they discharge often untreated sewage containing organic micropollutants. Although degradation of these pollutants by microorganisms is limited by the cold conditions, other pathways such as photodegradation may be significant. Our results indicate that, during the summer, photolysis is a potentially significant degradation pathway for organic micropollutants in Antarctic surface waters, although the rate of loss would depend on ice cover and water depth. Abstract Knowledge of the environmental fate of organic micropollutants in Antarctica is limited, especially with respect to photolysis. The Antarctic is characterised by extreme light conditions of either continuous sunshine or darkness depending on the season. The photolytic degradation of benzophenone-3 (BP-3), bisphenol A (BPA), 17α-ethinylestradiol (EE2), methyl paraben (mParaben), 4-t-octylphenol (4-t-OP) and triclosan in MilliQ and seawater was investigated over a range of irradiance levels and temperatures. Photodegradation was compound specific. Up to 20% of BPA, BP-3 and EE2 was degraded over a 7-h irradiance period. Triclosan and 4-t-OP degraded to below the limit of detection in all experiments whereas mParaben was not degraded. The degradation of triclosan increased with irradiance in both MilliQ (P=2.2×10-16) and seawater (P=2.2×10-16). The degradation of 4-t-OP increased with irradiance in MilliQ (P=8.5×10-9) and seawater (P=1.1×10-5), and with temperature in MilliQ (P=8.5×10-9) and seawater (P=1.0×10-5). Similar relationships could not be established for BPA, BP-3, EE2 and mParaben due to the limited extent of degradation observed. The photolysis of triclosan was enhanced 4-fold in seawater compared to MilliQ water. Results from this study indicate that micropollutants may persist for extended periods of time in Antarctic coastal waters, particularly with ice cover, above and beyond that exhibited in temperate seawater.

Environmental context Benzotriazoles are chemicals widely used to inhibit corrosion in various industrial processes and in household products. They persist in aquatic environments, even under UV irradiation, and thus there is a need to improve their photolytic degradation to minimise the environmental exposure risks. We investigated the effects of four iron–carboxylate complexes on the UV photodegradation of three benzotriazoles in aqueous solutions and show that they significantly increase the degradation rates of benzotriazoles. Abstract The effects of FeIII–carboxylate complexes on the photodegradation of three benzotriazoles (BTs), i.e. benzotriazole (BT), 5-methylbenzotriazole (5-TTri) and 5-chlorobenzotriazole (CBT) in aqueous solutions were investigated under exposure to UV irradiation at 254nm in the presence of FeIII and four carboxylate ions (oxalate, tartrate, succinate and citrate). The results showed that the presence of FeIII–carboxylate complexes significantly enhanced the photodegradation rates of all three selected BTs. The photodegradation of BT, 5-TTri and CBT followed first-order reaction kinetics with half-lives ranging from 0.57 to 3.98h for BT, 6.08 to 8.25h for 5-TTri and 2.63 to 5.50h for CBT in the four systems of the FeIII–carboxylate complexes. In comparison, the half-lives ranged between 3.40 and 4.81h for BT, 6.42 and 11.55h for 5-TTri and 4.13 and 6.79h for CBT in pure aqueous solution and in the presence of FeIII or carboxylate. The degradation rates of these BTs were dependent on the pH values, type of carboxylate and FeIII/carboxylate ratios. Both BT and CBT showed the highest photodegradation rates with the shortest respective half-lives of 0.57 and 2.63h at the initial FeIII/oxalate ratio of 10/200µmolL-1 in aqueous solutions at pH 3, whereas 5-TTri had the highest photodegradation rate with the shortest half life of 6.08h at the initial FeIII/succinate ratio of 10/10µmolL-1.

Environmental context Coal seam gas reserves are likely to make a major contribution to future energy needs. However, the new technology for exploiting these reserves, termed hydraulic fracturing, raises several environmental issues. We discuss the research required to assess the ecological risks from gas recovery. Abstract Coal seam gas reserves represent a major contribution to energy needs, however, gas recovery by hydraulic fracturing (fracking or fraccing), requires management to minimise any environmental effects. Although the industry is adapting where possible to more benign fracking chemicals, there is still a lack of information on exposure to natural and added chemicals, and their fate and ecotoxicity in both the discharged produced and flow-back waters. Geogenic contaminants mobilised from the coal seams during fracking may add to the mixture of chemicals with the potential to affect both ground and surface water quality. The research needs to better assess the ecological risks from gas recovery are discussed.

Environmental contextThe environmental fate of a particular contaminant can be influenced by the presence of other chemicals. It is shown that the photodegradation in water of benzotriazole, a common household and industrial chemical, is reduced in the presence of a sunscreen compound. Thus, contaminants such as benzotriazole may persist longer in the environment in the presence of chemicals designed to filter ultraviolet rays, such as those used in sunscreens. AbstractThe presence of co-solutes (e.g. UV filters) can potentially influence the environmental fate of micropollutants. The photolysis of benzotriazole (BT, an anticorrosion agent) and benzophenone-3 (BP-3, a UV filter), as well as their interactions in aqueous solutions under UV and artificial solar light with or without added humic acid (HA) and metal ions (Cu2+ and Fe3+), has been investigated. BT was found to be photosensitive under UV irradiation, but photostable under solar light. The half-lives for the photolysis of BT were 2.8h in pure aqueous solution and increasing to 4.5h in the presence of BP-3 (1.0mgL-1). BP-3 was photostable under both UV and artificial solar light. Solar radiation exposure of 50 days resulted in a small loss of BP-3 (8%) in pure aqueous solution, and resulted in a greater loss of BP-3 (up to 31%) at 50mgL-1 of HA. UV irradiation of the BT solutions containing BP-3 led to formation of five photoproducts, formed mainly by N–N and N–NH bond scission, polymerisation and hydroxylation. In the case of BP-3, one major photoproduct was isolated and tentatively identified as 2,4-dimethylanisole, formed by the loss of hydroxy and benzoyl groups.

Environmental contextBenzotriazole is an anti-corrosion agent that is widely applied in various industrial processes and in household products. It has been found persistent in various aquatic environments. Our investigation found that benzotriazole can be rapidly transformed under UV light to form several photoproducts. Photolysis rates decreased with increasing solution pH, whereas salinity had no significant effect. Metal species Cu2+and Fe3+, and humic acid in aquatic environment could have inhibitory effects on the photolysis of benzotriazole.AbstractBenzotriazole (BT) is an anti-corrosion agent used widely in some industrial processes and household products, and it has been detected in surface water and ground water due to its high mobility and low biodegradability. We have investigated the photolysis of benzotriazole in aqueous solutions under UV radiation at 254nm and the effect of pH, salinity, metal species and dissolved organic matter on the photo-transformation processes. Benzotriazole was found to undergo rapid transformation to form several photoproducts. The half-lives for the photolysis of benzotriazole ranged from 2.8 to 14.3h in various aqueous solutions containing metal ions and dissolved organic matter. Photolysis rates decreased with increasing solution pH, whereas salinity had no significant effect. Metal species Cu2+and Fe3+, and especially humic acid had inhibitory effects on the photolysis of benzotriazole under UV light irradiation at 254nm. We propose the formation of three major photoproducts via instantaneous polymerisation of small intermediates generated during the photolysis of benzotriazole including 2,6-diethylaniline, phenazine and 1,6-dihydroxyphenazine.

The role of biochar in sequestration of carbon, reducing the emission of greenhouse gases, and improving the soil fertility is increasingly being recognised and is leading to the recommendations of biochar amendment of soils. However, the implications of such amendments to the environmental fate and efficacy of pesticides are not well understood. The published work on the role of black carbon (which includes charcoal, soot, and other pyrolytic carbon materials) in the environmental fate and effect of organic contaminants is reviewed here, together with the studies on bioavailability and efficacy of some herbicides in soils amended with freshly produced biochars. Biochars, due to their unique properties especially their highly carbonaceous and aromatic nature and high specific surface area, have been reported to be up to >2000 times more effective than soil in sorbing pesticides. The incorporation of relatively small amounts of fresh biochars in soil (0.05% by wt) has also been shown to inhibit the microbial degradation of organic compounds including pesticides as well as reduce their plant availability and efficacy. Based on limited published research on biochars and related research on black carbon reviewed here, biochar amendments to soils are likely to reduce the bioavailability and efficacy of pesticides. Furthermore, these amendments can influence the potential accumulation and ecotoxicological impact of pesticides and other organic contaminants in the soil environment. The implications of heterogeneity and ageing of biochars applied to soils for sorption and desorption processes and in turn for other environmental fate processes need to be understood to seek the appropriate balance between carbon sequestration and pesticide efficacy. While biochar amendment of soil holds appeal from a carbon accounting and soil conditioning perspective, further research is urgently required to determine how biochar influences the efficacy and environmental fate of agrochemicals such as pesticides.

Environmental context.Due to the increasing adoption of nanotechnology, synthetic nanoparticles such as fullerenes (nC60), are likely to emerge as contaminants in aquatic and terrestrial environments. Currently, our understanding of the fate and effects of C60in the terrestrial environment is poor and is primarily hampered by the lack of reliable quantitative analytical methods. In this paper, we describe a method for effective extraction and sensitive detection of C60residues in soils which will facilitate environmental fate studies on nC60. Abstract.Fullerenes (e.g. C60) are emerging as environmental contaminants due to their wide range of applications, such as in optics, electronics, cosmetics and biomedicine. Residue analysis is a crucial step in understanding the fate and effects of C60in the terrestrial environments. However, there is a lack of reliable quantitative analytical methods for extraction and analysis of C60in soils or sediments. We developed a method for determination of C60in soils using accelerated solvent extraction (ASE) followed by HPLC-UV detection. Separation of C60from soil matrix interferences was achieved by gradient elution using methanol–toluene mobile phase. Mean recoveries obtained from extraction efficiency tests using six contrasting soils spiked (wet and dry tests with freeze drying of wet and aged soils before ASE) at varying concentrations of C60ranged from 84 to 107%. The current method provides adequate sensitivity (limit of quantitation = 20 μg kg-1), and can be used for quantitative determination of C60in soils and sediments (especially for environmental fate studies) without needing expensive HPLC-mass spectrometry.

Off-site movement of nutrients and sediment from furrow-irrigated agriculture has been a concern in the Ord River Irrigation Area, Western Australia. After consultation with growers, a range of management strategies were tested to assess the effectiveness of various practices to minimise off-site movement of nutrients during irrigation. This paper reports on the effectiveness of the additions of high molecular weight, anionic, polyacrylamide (PAM) to irrigation water to minimise off-site movement of phosphorus, nitrogen, carbon, and sediment. Surface runoff water quantity and quality from 4 separate irrigation bays, which contained 25 furrows per irrigation bay, was monitored over time for a single irrigation 35 days after sowing.  Addition of PAM as a puck (cylindrical disc 55mm diameter by 23mm height) to the head of each irrigation furrow significantly (P < 0.001) decreased the average volume of surface runoff water leaving the irrigation bays by 54%, from 599kL for the control irrigation bays to 277kL for the PAM-treated irrigation bays. The addition of PAM also significantly (P < 0.001) decreased the average total suspended sediment load for the duration of the irrigation from 94.9kg/ha for the control bays to 13.4kg/ha for the PAM-treated irrigation bays. The concentrations of the different forms of N, P, and C measured in the runoff water were not significantly different between the 2 treatments. The amounts (g) of particulate (>0.45m) P and dissolved organic C were significantly (P < 0.01) less from the PAM-treated bays than from the control bays.  There was a consistent trend for the addition of PAM to decrease the cumulative mass loss of all nutrients (N, P, and C) measured. However, significant decreases were only seen for particulate (>0.45m) P (by 94%), unfiltered (or total) N (by 56%), and unfiltered (or total) C (by 60%). This experiment demonstrated that the addition of PAM to irrigation waters has the potential to decrease the off-site movement of nutrients bound to colloidal material. However, in this study off-site movement of contaminants present in the ?soluble' (<0.45m) fraction is unlikely to be mitigated by the addition of PAM to irrigation water. The mode of application of PAM, however, may affect water infiltration and hence vertical movement of ?soluble' contaminants and requires further investigation to ensure that while off-site surface transport is being minimised, contamination of groundwater is not being increased. Other strategies to minimise off-site movement for contaminants in the dissolved phase also need investigation.

Off-site movement of pesticides from furrow-irrigated agriculture has been a concern in the Ord River Irrigation Area, Western Australia. After consultation with growers a range of management strategies were tested to assess the effectiveness of various practices to minimise off-site movement of pesticides during irrigation. This paper reports on the effectiveness of the additions of high molecular weight, anionic, polyacrylamide (PAM) to irrigation water to minimise off-site movement of endosulfan, chlorothalonil, bupirimate, and atrazine. Water leaving from 4 separate irrigation bays, which consisted of 25 furrows per irrigation bay (Expt 1) or 39 furrows per irrigation bay (Expt 2), was monitored over time. The average concentration of endosulfan ? and ? and bupirimate leaving the irrigation bays for the duration of the single irrigation event was generally always less for the PAM-treated irrigation bays than the control (control treatment). The addition of PAM to the irrigation water significantly decreased the cumulative runoff losses (g) of total endosulfan by 54% from 11.41 to 5.19g/ha (P<0.05), and of chlorothalonil by 49% from 53.65 to 27.32g/ha (P<0.001). There was no statistical difference in the load of atrazine or bupirimate leaving either treatment. Although the addition of PAM to irrigation water effectively decreased the off-site movement of 2 fairly strongly sorbed pesticides, endosulfan and chlorothalonil, it did not decrease the total load moving off-site of the more weakly sorbed pesticides, bupirimate and atrazine. The addition of PAM as a liquid to irrigation water was not found to increase the infiltration of a soluble pesticide, atrazine, into the soil profile. The mode of application of PAM, however, may affect water infiltration and hence vertical movement of soluble pesticides and requires further investigation.

Determination of sorption of hydrophilic, weakly sorbing organic compounds in soil by conventional batch methods using a slurried suspension is often prone to considerable errors because small changes in the solution concentration on equilibration must be accurately determined. This difficulty is exacerbated for compounds susceptible to degradation, which also decreases the solution concentration. The objective of this study was to determine sorption of hydrophilic pesticides by applying an unsaturated transient flow method, which enables determination of sorption at sufficiently small solution to soil ratios. The method makes use of piston‐like displacement of the antecedent solution in equilibrium with sorbed phase when pesticide‐free water is infiltrated into a soil column spiked with a pesticide. Pesticide sorption and the solution concentration are inferred from a plot of total pesticide content per unit mass of soil vs. water content in a region where the antecedent solution is accumulated. Thus, extraction of solution from relative dry soil is unnecessary. We tested this method for two hydrophilic pesticides, monocrotophos [dimethyl (E)‐1‐methyl‐2‐(methyl‐carbamoyl) vinyl phosphate] and dichlorvos (2,2‐dichlorovinyl dimethyl phosphate). The sorption coefficient, Kd, obtained for monocrotophos was slightly lower than that by batch method (Kd= 0.10 vs. 0.19 L kg−1), whereas for dichlorvos, a compound highly susceptible to degradation, the unsaturated flow method yielded a much smaller Kd(0.19 vs. 3.22 L kg−1). The Kdvalues for both compounds were consistent with the observed retardation in the pesticide displacement in the columns. The proposed method is more representative of field conditions and particularly suitable for weakly sorbing organic compounds in soils.

A chromatographic model (VARLEACH) and a process-based model (LEACHM) were evaluated under low and high water input regimes (‘rainfall’ and ‘rainfall + irrigation’, respectively) using experimental data for a non-reactive tracer (KBr), and 3 sulfonylurea herbicides: triasulfuron, metsulfuron-methyl, and chlorsulfuron. Both qualitative and quantitative comparisons of predicted and measured water contents revealed that both models performed well under ‘rainfall’, but prediction was less satisfactory under the treatment of ‘rainfall &plus; irrigation’. Both models failed to simulate the bimodal distribution of Br - and the herbicides observed under ‘rainfall &plus; irrigation’ treatment. Distribution of Br - and the 3 herbicides in the profile was over- or under-estimated at certain depths and times, probably due to the limitations inherent to the models (e.g. inability to deal with the macropore flow), and to simplifications associated with some input data. Simulations for a dry (1 decile), median (5 decile), and wet year (9 decile) with LEACHM and VARLEACH models using long-term weather data for the site showed that leaching and persistence of the herbicides are highly dependent on the amount of rainfall the site receives. The results indicate that the risk of injury to herbicide-sensitive crops in the following year of application of herbicides is likely to be greater when the herbicides are applied in a drier rather than a wetter year. simulation, herbicide persistence, transport, modelling efficiency.

Organophosphorus, pyrethroid and chloronicotinyl insecticides have been used to control termites in building structures in recent years. We investigated the degradation behaviour of three insecticides (bifenthrin, chlorpyrifos and imidacloprid) at termiticidal application rates under standard laboratory conditions (25 °C, 60% field moisture capacity and darkness) for 24 months. The study was carried out on one soil and two bedding materials (sand-dolomite and quarry sand), which are commonly used under housing in Australia. Experiments were also conducted to examine the effect of soil moisture on the degradation of these insecticides. Insecticide residues in the samples collected at different days after application were measured by high performance liquid chromatography (HPLC). The rate of degradation of bifenthrin and imidacloprid insecticides was adequately described by a first-order kinetic model (r² = 0.93–0.97). However, chlorpyrifos degradation was biphasic, showing an initial faster degradation followed by a slower rate. Therefore, the degradation data during the slower phase only (after a two-month period) followed the first-order law (r² = 0.95). Soil moisture had little effect on degradation of imidacloprid and bifenthrin. Among the three insecticides, bifenthrin and imidacloprid were most stable and chlorpyrifos the least. Chlorpyrifos showed a major loss (75–90%) of residue during the 24 months incubation period. In the bedding materials, simultaneous accumulation of the primary metabolite of chlorpyrifos, TCP (3,5,6-trichloro-2-pyridinol) was observed. Hydrolysis appeared to have caused the observed rapid loss of chlorpyrifos, especially in the highly alkaline bedding materials (sand-dolomite and quarry sand). © 1999 Society of Chemical Industry

Sorption nonequilibrium of pesticides in soil is relatively less understood compared with equilibrium sorption. Furthermore, batch techniques generally used in kinetic studies do not represent field conditions. Flow techniques, on the other hand, closely represent pesticide transport and have many advantages over batch techniques. A flow technique was used to study the sorption kinetics of three pesticides in four Western Australian soils. Sorption data of all pesticides showed an initial rapid rate followed by a slower rate of sorption. While a first-order equation failed to satisfactorily describe the sorption data, both the Freundlich two-site kinetic equation and the parabolic diffusion law fitted well to the data. The rapid component of sorption varied from 0 to 25 of total sorption (24 h sorption value) for various pesticides. A comparison of sorption data obtained by a batch technique and a flow technique revealed that sorption occurs at a much faster rate under batch conditions, presumably because of shaking and high solution to soil ratio. Under batch conditions, the instantaneous component of sorption was very high (up to 90 of 24-h sorption value). The characteristics of the soil also affected the rate of sorption of the pesticides. A well structured soil with high organic matter content showed slower rate of sorption compared with a dispersed soil with low organic matter content.

Rate coefficients describing sorption of pesticides in soils are commonly obtained under well stirred conditions from batch equilibration studies. Batch techniques involve high solution-to-soil ratios and mechanical agitation, both of which can influence the sorption characteristics of a soil. In addition, rapid equilibration cannot be studied accurately in batch experiments. These disadvantages can, however, be overcome by studying the sorption of pesticides during leaching in saturated columns of soil. Results in this paper show how time-dependent sorption of pesticides in soil can be calculated by applying the peak maxima method from the gas-chromatographic literature to pesticide breakthrough curves of short pulse injections in soil columns.

The sulfonylurea herbicides comprise a group of compounds designed to control broad-leaved weeds and some grasses in a variety of crops. The herbicides have become popular because of their low application rates (10-40 g/ha), low mammalian toxicity, and unprecedented herbicidal activity. We present a review of the fate and behaviour of these herbicides in soils with particular reference to alkaline soils of Australia. The review shows that the low application rates of sulfonylurea herbicides continue to present an analytical challenge, although in recent years a number of new methods capable of detecting them at very low concentrations have been developed. A range of analytical methods is available, including high performance liquid chromatography, gas chromatography, immunoassay, and bioassay. However, analytical sensitivity required to detect trace levels of these herbicides continues to pose problems in routine detection of herbicide residues in soils. The review reveals that there are no reports of studies of the behaviour of sulfonylureas in soils with pH >8·2. This is of particular significance to Australian conditions because a number of Australian soils are even more alkaline, and the pH(water) in subsoils can be as high as 10· 2. Sorption of sulfonylureas is pH-dependent and has a strong negative correlation with pH. At pH >8·0 sorption is very low. In acid soils, however, sorption of chlorsulfuron, metsulfuron-methyl, and triasulfuron is strongly influenced by the soil temperature, clay content, and, particularly, organic matter content. The principal modes of degradation of the herbicides are acid hydrolysis and microbial degradation with the latter being the only major pathway in alkaline soils. Hydrolysis of the sulfonylureas is more rapid under acidic conditions (pH 4{7), and the data suggest that hydrolysis is likely to be very slow in alkaline soils. Data from other countries suggest that the half-life of chlorsulfur on increases exponentially with pH, and that it is also influenced by variations in the temperature and water content of the soil. Being acidic in nature, the herbicide molecules become anionic at high pH and can move to a considerable depth in the soil profile by leaching. Movement of the sulfonylureas in soil is largely influenced by organic matter content and soil pH and the reviewed data show that sulfonylureas have substantial leaching potential in the sandy alkaline soils of Australia. This is likely to result in increased persistence in alkaline subsoils lacking in organic matter and biological activity. Computer models to predict the persistence and movement of the sulfonylureas are available; however, additional input parameters are required to predict accurately the behaviour of specific herbicides in alkaline soils under Australian conditions. Since new herbicides with chemistry similar to existing sulfonylureas are increasingly likely to be available for use, there is a need to develop comprehensive understanding of their fate, behaviour, and impact on Australian cropping and ecological systems. sorption, degradation, leaching, sulfonylureas, hydrolysis, models, alkaline soils.

Fenamiphos is an important nematicide{insecticide and commonly used in horticultural crops and turfs in Australia. We studied the transformation/degradation of fenamiphos under controlled conditions, in surface and subsurface soils from the Swan Coastal Plain of Western Australia. In the sandy surface soil, fenamiphos (Fen) was rapidly oxidised to its sulfoxide (FenSO) analogue. Further oxidation of FenSO to sulfone (FenSO2), however, was found to be very slow, resulting in an accumulation of FenSO. Little accumulation of FenSO2 occurred during the study period (139 days). The time taken for 50% loss of the total residue of fenamiphos (Fen+FenSO+FenSO2) was found to be approximately 50 days in the surface soil and about 140 days in the subsurface soil. Simulations using the LEACHM model showed that the rate of transformation of Fen to FenSO in the surface soil (k1 = 0·5/day) was 100 times faster than that of FenSO to FenSO2 (k2 = 0·005/day). In the subsurface soil, the difference between the 2 oxidation steps was much smaller (4-fold). The conversion of Fen to FenSO was much faster in the surface soil (k1 = 0·5/day) than the subsurface soil (k1 = 0·02/day). The observed differences in transformation behaviour of Fen between the surface and subsurface layers of soil appear to be associated with the differences in the microbial biomass and the organic matter contents of the soils. The slower transformation of Fen in the subsurface soils can have major implications on its potential for groundwater contamination in vulnerable areas, such as the Swan Coastal Plain of Western Australia. organophosphates, pesticide, oxidation, hydrolysis, LEACHM.