Lester Smith

Poor efficacy of herbicides in biochar-amended soils as affected by their chemistry and mode of action

We evaluated wheat straw biochar produced at 450°C for its ability to influence bioavailability and persistence of two commonly used herbicides (atrazine and trifluralin) with different modes of action (photosynthesis versus root tip mitosis inhibitors) in two contrasting soils. The biochar was added to soils at 0%, 0.5% and 1.0% (w/w) and the herbicides were applied to those soil-biochar mixes at nil, half, full, two times, and four times, the recommended dosage (H(4)). Annual ryegrass (Lolium rigidum) was grown in biochar amended soils for 1 month. Biochar had a positive impact on ryegrass survival rate and above-ground biomass at most of the application rates, and particularly at H(4). Within any given biochar treatment, increasing herbicide application decreased the survival rate and fresh weight of above-ground biomass. Biomass production across the biochar treatment gradient significantly differed (p<0.01) and was more pronounced in the case of atrazine than trifluralin. For example, the dose-response analysis showed that in the presence of 1% biochar in soil, the value of GR(50) (i.e. the dose required to reduce weed biomass by 50%) for atrazine increased by 3.5 times, whereas it increased only by a factor of 1.6 in the case of trifluralin. The combination of the chemical properties and the mode of action governed the extent of biochar-induced reduction in bioavailability of herbicides. The greater biomass of ryegrass in the soil containing the highest biochar (despite having the highest herbicide residues) demonstrates decreased bioavailability of the chemicals caused by the wheat straw biochar. This work clearly demonstrates decreased efficacy of herbicides in biochar amended soils. The role played by herbicide chemistry and mode of action will have major implications in choosing the appropriate application rates for biochar amended soils.

Speciation of arsenic in ground water samples: A comparative study of CE-UV, HG-AAS and LC-ICP-MS

The performance of capillary electrophoresis-ultraviolet detector (CE-UV), hydride generation-atomic absorption spectrometry (HG-AAS) and liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS) have been compared for the speciation of arsenic (As) in groundwater samples. Two inorganic As species, arsenite (As(III)), arsenate (As(V)) and one organo species dimethyl arsenic acid (DMA) were mainly considered for this study as these are known to be predominant in water. Under optimal analytical conditions, limits of detection (LD) ranging from 0.10 (As(III), AsT) to 0.19 (DMA) mug/l for HG-AAS, 100 (As(III), DMA) to 500 (As(V)) mug/l for CE-UV and 0.1 (DMA, MMA) to 0.2 (As(III), As(V)) mug/l for LC-ICP-MS, allowed the determination of the above three species present in these samples. Results obtained by all the three methods are well correlated (r(2)=0.996*** for total As) with the precision of <5% R.S.D. except CE-UV. The effect of interfering ions (e.g. Fe(2+), Fe(3+), SO(4)(2-) and Cl(-)) commonly found in ground water on separation and estimation of As species were studied and corrected for. Spike recovery was tested and found to be 80-110% at 0.5mug/l As standard except CE-UV where only 50% of the analyte was recovered. Comparison of these results shows that LC-ICP-MS is the best choice for routine analysis of As species in ground water samples.

Arsenic in Australian Environment: An Overview

Abstract The most common source of elevated As concentrations in the Australian environment are attributable to anthropogenic activities. Mining activities have contributed to the contamination of soil and water primarily in Western Australia and Victoria. However, other anthropogenic activities such as agriculture, forestry and industry have also contaminated soil and water at a localized scale. Currently there are over 1000 As contaminated sites previously used as cattle dips for eradicating cattle ticks. Although As contamination of the environment may be severe enough to limit plant growth there appears to be few other reports identifying the impacts of the contaminants on other organisms, such as fish, mammals and humans. In Australia the impacts of metal/metalloid contamination of the environment are often unnoticed or ignored. However, the impacts of elements such as As may pass unnoticed by the public or regulators due to the perception of the minimal impact a contaminant has on the environment. This paper presents an overview of As in the Australian environment including the sources of As contamination, soil, water and plant As content, and the pathways of exposure.

Method for assessing plant-available cadmium in soils

The suitability of several extractants was tested for assessing the plant-available cadmium (Cd) in a few selected soils of South Australia. The amount of Cd extracted by 7 extractants (0.01 and 0.05 M CaCl 2 , Na 2 EDTA, DTPA-TEA, M NH 4 NO 3 , AAAC-EDTA, and M NH 4 Cl) was related to the Cd concentration in the stem and leaves of durum wheat (Triticum aestivum L. var. Excalibur) grown in the greenhouse for 5 weeks. Soil extraction with M NH 4 Cl gave the best overall prediction of extractable Cd with plant Cd concentration (r = 0.928, P < 0.001) compared with the other extractants. Multivariate models were derived to predict both the total and plant-available Cd from the soil factors. The aqua-regia-extractable Cd was on an average 45.3% of the total Cd content, as determined by HF-HClO 4 digestion, and at best could represent the easily extractable fraction of soil Cd. Around 77% of the variation in total Cd content of the soils could be explained using selected soil properties, such as free Fe, organic C, and pH. The accumulation of Cd by wheat plants from the soils studied could be assessed using the multivariate model, log leaf Cd = – 0.2107 + 1.2281 log Cd NH 4 Cl, with high correlation (R 2 = 0.93). The coefficient of determination could be improved further (R 2 = 0.99) with the inclusion of the soil variables free Fe, pH, organic C, and clay contents: log leaf Cd = 0.2095 + 1.2556 log Cd NH 4 Cl + 0.0219 Fe + 0.0149 clay – 0.2633 org. C – 0.0577 pH.

Effects of electrolyte composition on chromium desorption in soils contaminated by tannery waste

We conducted batch studies to investigate the effect of phosphate and dominant cations present in tannery waste on desorption of chromium (Cr) from surface and subsurface soil horizons from a contaminated tannery waste site at Mount Barker, South Australia. The surface horizon (0–15 cm) of the soil profile was alkaline (pH 7.9) and the subsurface horizon (50–90 cm) was acidic (pH 3.9). Aqua-regia extractable Cr concentration ranged from 62 g/kg in the surface to 0.26 g/kg in the subsurface soils. X-ray diffraction and scanning electron microscopic studies revealed the predominance of carbonate and kaolin minerals in the surface soils, and highly weathered framboidal particles, with morphology similar to that of pyrites, in the subsurface soils. The amount of Cr desorbed from the contaminated soils varied considerably with both the electrolyte’s cationic charge and soil properties. The effect of cations, Ca 2+ and Na + (CaCl 2 , NaCl), and phosphate on desorption of Cr was investigated. While the ionic strength of the solutions was standardised at approximately 0.03 mol/L, the concentration of phosphate (as KH 2 PO 4) was varied from 0 to 3.2 mmol/L. On the basis of studies on solution to soil ratio and desorption kinetics we chose a 20: 1 solution to soil ratio and 2 h equilibration time. In the surface alkaline soil, the amount of Cr released decreased in the order Na + (286 μg/L) ≥ water (256 μg/L) > Ca 2+ (156 μg/L). In contrast subsurface acidic soil showed a reverse trend, i.e. Ca 2+ (52 μg/L) > Na + (29 μg/L) > water (20 μg/ L). Speciation of Cr in the extracts showed predominantly Cr(VI) in the alkaline surface soil and Cr(III) in the subsurface acidic soil. A strong effect of phosphate on the cumulative amount of chromate desorbed was observed. The study shows that the presence of high concentrations of Na + (0.03 mol/L) and phosphate (3.2 mmol/L) in soil solution enhances Cr(VI) mobility. In contrast, Ca 2+ may induce retention of Cr(VI) in Cr-contaminated alkaline soils.

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.

Contrasting effects of two antimicrobial agents (triclosan and triclocarban) on biomineralisation of an organophosphate pesticide in soils.

We examined the impact of triclosan (TCS) and triclocarban (TCC) antimicrobial compounds on the biomineralisation of glucose and cadusafos pesticide in three Australian soils. Mineralisations of radiolabelled ((14)C) compounds were measured over a period of up to 77 d in sterile and non-sterile soils treated with different concentrations of TCS and TCC (0-450 mg kg(-1)). The rates of mineralisation of cadusafos were found to decrease with increasing concentration of TCS in all soils, but varied with soil type. Soils treated with TCS at the highest concentration (270 mg kg(-1)) reduced cadusafos mineralisation by up to 58%. However, glucose mineralisation was not significantly affected by the presence of TCS. While TCS, significantly reduced the mineralisation of cadusafos (by 17%; p<0.05) even at the lowest studied concentration (30 mg kg(-1)), no significant effect of TCC was observed on cadusafos or glucose mineralisation even at the highest concentration used (450 mg kg(-1)).