Peter Lockwood

The chemistry and behaviour of antimony in the soil environment with comparisons to arsenic: A critical review

This article provides a critical review of the environmental chemistry of inorganic antimony (Sb) in soils, comparing and contrasting findings with those of arsenic (As). Characteristics of the Sb soil system are reviewed, with an emphasis on speciation, sorption and phase associations, identifying differences between Sb and As behaviour. Knowledge gaps in environmentally relevant Sb data for soils are identified and discussed in terms of the limitations this imposes on understanding the fate, behaviour and risks associated with Sb in environmental soil systems, with particular reference to mobility and bioavailability.

Adsorption of antimony(V) by floodplain soils, amorphous iron(III) hydroxide and humic acid

Antimony (Sb) emissions to the environment are increasing, and there is a dearth of knowledge regarding Sb fate and behaviour in natural systems. In particular, there is a lack of understanding of sorption of the oxidised Sb(V) species onto soils and soil phases. In this study sorption of Sb(V) by two organic rich soils with high levels of oxalate extractable Fe was examined over the pH range of 2.5-7. Furthermore, the sorption behaviour of Sb(V) was examined in two phases mimicking those dominant in the experimental soils, namely a solid humic acid and an amorphous Fe(OH)3, across the same pH range. Sorption of Sb by the soils and the humic acid fitted a Freundlich type isotherm, with the equation parameters reflecting changes in bonding affinity corresponding to pH changes. The soils sorbed >75% of the added Sb in all trials, and 80-100% at pH values less than approximately 6.5. The Fe(OH)3 retained >95% of the added Sb in all experiments. The humic acid sorbed up to 60% of the added Sb at acidic pH values, but sorption decreased to zero at higher pH values. Further adsorption studies are recommended, such as examining the effects of ion competition and changes in ionic strength.

Bioaccumulation of antimony and arsenic in a highly contaminated stream adjacent to the Hillgrove Mine, NSW, Australia

Environmental context. Concern over the presence of antimony (Sb) in the environment because of chemical similarities with arsenic (As) has prompted a need to better understand its environmental behaviour and risks. The present study investigates the bioaccumulation and uptake of antimony in a highly contaminated stream near the Hillgrove antimony–gold mine in NSW, Australia, and reports high Sb (and As) concentrations in many components of the ecosystem consisting of three trophic levels, but limited uptake into aboveground parts of riparian vegetation. The data suggest that Sb can transfer into upper trophic levels of a creek ecosystem, but that direct exposure of creek fauna to creek sediment and soil, water and aquatic autotrophs are more important metalloid uptake routes than exposure via riparian vegetation. Abstract. Bioaccumulation and uptake of antimony (Sb) were investigated in a highly contaminated stream, Bakers Creek, running adjacent to mining and processing of Sb–As ores at Hillgrove Mine, NSW, Australia. Comparisons with arsenic (As) were included owing to its co-occurrence at high concentrations. Mean metalloid creek rhizome sediment concentrations were 777 ± 115 μg g–1 Sb and 60 ± 6 μg g–1 As, with water concentrations at 381 ± 23 μg L–1 Sb and 46 ± 2 μg L–1 As. Antimony and As were significantly elevated in aquatic autotrophs (96–212 μg g–1 Sb and 32–245 μg g–1 As) but Sb had a lower uptake efficiency. Both metalloids were elevated in all macroinvertebrates sampled (94–316 μg g–1 Sb and 1.8–62 μg g–1 As) except Sb in gastropods. Metalloids were detected in upper trophic levels although biomagnification was not evident. Metalloid transfer to riparian vegetation leaves from roots and rhizome soil was low but rhizome soil to leaf As concentration ratios were up to 2–3 times greater than Sb concentration ratios. Direct exposure to the rhizosphere sediments and soils, water ingestion and consumption of aquatic autotrophs appear to be the major routes of Sb and As uptake for the fauna of Bakers Creek.

Comparison of Digestion Methods for ICP-OES Analysis of a Wide Range of Analytes in Heavy Metal Contaminated Soil Samples with Specific Reference to Arsenic and Antimony

Abstract Recommended alternative digestion methods for elemental analysis of soil often omit arsenic (As) and antimony (Sb) as viable analytes. In addition, comparisons of these methods for analysis of a wide range of elements by ICP-OES are few, limiting the viability of recommended methods. Four methods for the digestion of soils (microwave aqua regia, open aqua regia, microwave nitric, and open nitric) were assessed in seven field soil samples analyzed by ICP-OES. Relative extraction strength and analytical precision were compared for 18 elements [aluminum (Al), iron (Fe), manganese (Mn), magnesium (Mg), calcium (Ca), potassium (K), phosphorus (P), sulfur (S), arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), sodium (Na), nickel (Ni), lead (Pb), antimony (Sb), and zinc (Zn)] with the emphasis on obtaining optimal analytical results for the volatiles As and Sb. The microwave aqua regia digestion was found to give better elemental extraction and analytical variability for the widest range of analytes, with acceptable results for As and Sb. This method was found to give adequate recoveries for most analytes (excluding Ni, Cr, Co, and Na), and good precision in the analysis of standard material and further field samples (relative standard deviation <20%). The microwave aqua regia method used was determined to be a better multi-element (including As and Sb) alternative to the open aqua regia method than the current Australia and New Zealand (ANZECC) recommended alternative of microwave nitric digestion.

Measurement of chemical weathering rates using natural chloride as a tracer

The rates of chemical weathering within forested catchments as reported in the literature have been determined principally from input-output budgets, with outputs being measured as streamflow at a weir. In the present study an alternative method has been investigated which uses natural chloride as a tracer and does not require construction of a weir. It is shown that estimates made of weathering release rates of the cations Na+, K+, Ca2+, Mg2+ using the chloride tracer method are generally less affected by unmeasured deep seepage losses from the catchment or changes in groundwater storage than those using the weir method. The chloride tracer method could permit estimates of weathering rates to be made more frequently than at present in studies of forest nutrient cycling. Weathering rates were measured in four forested catchments with annual rainfall up to about 2000 mm, lying mostly within the Mount Boss state Forest near Wauchope, NSW. The forest is a mixture of rainforest and moist hardwood forest, parts of which are regenerating after logging. Porphyritic rhyodacite underlies all the catchments and has produced red and yellow acid soils (Dystrochrepts). Cation:chloride ratios in streamwater varied little over time, and showed little if any dependence on streamflow. “Grab” samples could be used in the estimation of weathering rates. The average weathering release rates in the major catchments sampled at Mount Boss for Na, K, Ca and Mg were 10.4, 5.3, 6.0 and 2.2 kg ha−1 yr−1 respectively. The average rock weathering rate for the same catchments calculated from Na release was 450 kg ha−1 yr−1 and from Ca was 340 kg ha−1 yr−1. Theoretical analysis of the effect of forest regeneration on weathering rate estimates from the chloride tracer method shows that the true rock weathering rate should lie between these two figures and was taken as 400 kg ha−1 yr−1.

Importance of Noncrystalline Hydroxide Phases in Sequential Extractions to Fractionate Antimony in Acid Soils

Abstract Sequential extraction techniques have been used to make inferences about speciation of phosphorus (P) and to a lesser extent arsenic (As) in soils. However, sequential extraction studies on the less‐abundant group V element, antimony (Sb), are limited. In this work, a widely used P sequential extraction scheme was modified and used to extract P, As, and Sb from two acidic soils from the Macleay River floodplain, NSW, that were enriched with Sb (26.9 and 23.0 mg kg−1). An ammonium oxalate–oxalic acid step was included in the extraction sequence to dissolve the noncrystalline iron (Fe) and aluminium (Al) hydroxide phase. It extracted 30 to 47% of Sb, indicating the importance of this fraction, which may be mobilized in the floodplain by acid sulfate soil processes and periodic waterlogging. The original method overestimated P, As, and Sb in the residual fraction (30–71%). Relative efficiency values of extracts for P, As, and Sb were compared, and inferences about phase distributions were made. The results suggest some potential in using extractions to assess bioavailability of Sb in soil.

Physical soil architectural traits are functionally linked to carbon decomposition and bacterial diversity

Aggregates play a key role in protecting soil organic carbon (SOC) from microbial decomposition. The objectives of this study were to investigate the influence of pore geometry on the organic carbon decomposition rate and bacterial diversity in both macro- (250–2000 μm) and micro-aggregates (53–250 μm) using field samples. Four sites of contrasting land use on Alfisols (i.e. native pasture, crop/pasture rotation, woodland) were investigated. 3D Pore geometry of the micro-aggregates and macro-aggregates were examined by X-ray computed tomography (μCT). The occluded particulate organic carbon (oPOC) of aggregates was measured by size and density fractionation methods. Micro-aggregates had 54% less μCT observed porosity but 64% more oPOC compared with macro-aggregates. In addition, the pore connectivity in micro-aggregates was lower than macro-aggregates. Despite both lower μCT observed porosity and pore connectivity in micro-aggregates, the organic carbon decomposition rate constant (Ksoc) was similar in both aggregate size ranges. Structural equation modelling showed a strong positive relationship of the concentration of oPOC with bacterial diversity in aggregates. We use these findings to propose a conceptual model that illustrates the dynamic links between substrate, bacterial diversity, and pore geometry that suggests a structural explanation for differences in bacterial diversity across aggregate sizes.

The availability and mobility of arsenic and antimony in an acid sulfate soil pasture system

The Macleay floodplain on the north coast of New South Wales, Australia, has surface soil concentrations of up to 40 mg kg(-1) arsenic (As) and antimony (Sb), due to historical mining practices in the upper catchment. The floodplain also contains areas of active and potential acid sulfate soils (ASS). Some of these areas are purposely re-flooded to halt oxidation processes, but the effect of this management on the metalloid mobility and phytoavailability of the metalloids present is unknown. This study investigated the changes to soil solution As and Sb, associations of metalloids with soil solid phases, and uptake into two common pasture species following 20 weeks of flooding in a controlled environment. The effect of an ASS subsoil was also investigated. The soil solution concentration and availability of the metalloids was in some instances higher in the floodplain soils than would generally be expected in soils with comparable contamination. There appeared to be few changes to soil solution concentrations or phase associations with flooding in this short term study, due to the high acid buffering and poise of the investigated soils. A strong relationship was found between the relative uptake of Sb into pastures and the oxalate extractable Fe in the soil, which was taken as a proxy for non-crystalline iron (Fe) hydroxides. This relationship was dependent on flooding and was absent for As. Further targeted investigations into metalloid speciation kinetics and the stability of soil solid phases with flooding management are recommended.

Effects of nutrient and lime additions in mine site rehabilitation strategies on the accumulation of antimony and arsenic by native Australian plants

The effects of nutrient and lime additions on antimony (Sb) and arsenic (As) accumulation by native Australian and naturalised plants growing in two contaminated mine site soils (2,735 mg kg(-1) and 4,517 mg kg(-1) Sb; 826 mg kg(-1) and 1606 As mgkg(-1)) was investigated using a glasshouse pot experiment. The results indicated an increase in soil solution concentrations with nutrient addition in both soils and also with nutrient+lime addition for Sb in one soil. Metalloid concentrations in plant roots were significantly greater than concentrations in above ground plant parts. The metalloid transfer to above ground plant parts from the roots and from the soil was, however, low (ratio of leaf concentration/soil concentration≪1) for all species studied. Eucalyptus michaeliana was the most successful at colonisation with lowest metalloid transfer to above ground plant parts. Addition of nutrients and nutrients+lime to soils, in general, increased plant metalloid accumulation. Relative As accumulation was greater than that of Sb. All the plant species studied were suitable for consideration in the mine soil phytostabilisation strategies but lime additions should be limited and longer term trials also recommended.

Impact of waterlogging on the nutrition of cotton (Gossypium hirsutum L.) produced in sodic soils

Abstract. Sodicity in Vertosols used for agricultural production can adversely affect the growth and nutrition of cotton (Gossypium hirsutum L.) plants. Cotton produced in sodic soils has reduced dry matter and lint yield and can develop toxic plant tissue concentrations of sodium (Na) but limited tissue concentrations of phosphorus (P,) potassium (K), and micronutrients. Crops produced on sodic soils frequently suffer from aeration stress after an irrigation or rainfall event, and it was hypothesised that the adverse physical and/or chemical conditions of sodic soils may exacerbate the effects of waterlogging. We measured the impacts of sodicity on the growth, nutrition, and root recovery time of cotton during and after waterlogging in two experiments. In the first, cotton plants were subjected to a 7-day period of inundation in Grey Vertosols with a range of exchangeable sodium percentage (ESP) values from 2 to 25%; 32P was placed in the pots and its accumulation in the plant was used to indicate root activity and recovery after the waterlogging event. In a second experiment, agar was dissolved in nutrient solutions with a range of Na concentrations (9, 30, and 52 mm) matching soil solution Na concentrations in sodic soils, in order to simulate a waterlogging event. Following the waterlogging event, the solutions were labelled with 32P, in order to determine the effect of sodic soil solution chemistry on the rate of recovery of cotton root function after the event. Plant nutrient analysis was used to determine the effects of sodicity and waterlogging on cotton nutrition. In both experiments, waterlogging reduced root activity and reduced the uptake and transport of labelled P by the cotton plants, decreased plant P and K concentrations, and increased the plant Na concentrations. Sodicity exacerbated the effects of waterlogging on root function and cotton nutrition in the soil experiment but not in the nutrient solution experiment, suggesting that any contribution of waterlogging to the patterns of nutrient accumulation in cotton crops produced in sodic fields occurs due to soil physical factors rather than soil solution chemistry.