Environmental Parameters Affecting the Concentration of Iodine in New Zealand Pasture.

Iodine (I) is an essential trace element commonly deficient in agricultural systems. Whereas there is much information on I in food crops, there is a lacuna of knowledge on the environmental factors that affect pasture I concentrations. We aimed to identify the most important environmental factors affecting the concentration of I in New Zealand pastures, and the consequences to agricultural systems. Soil and pastoral samples were collected throughout the country and analyzed for I and other elements. The soils contained 1.1 to 86 mg I kg, with 0.005 to 1.4 mg kg in the pasture. In 26% of pastures, I concentrations were insufficient for sheep nutrition, whereas 87% contained insufficient I for cattle nutrition. Pasture I concentrations were negatively correlated with the distance from the sea, and the concentration of oxalate-extractable amorphous Al, Fe, and Si oxides, which immobilize soil I. Soil organic C and clay increased I retention in soil but did not significantly affect pasture I concentrations. Future work should investigate how soil properties affect pasture I uptake in inland areas.

Lithium as an emerging environmental contaminant: Mobility in the soil-plant system.

Contamination of soil with lithium (Li) is likely to increase due to its wider dispersal in the environment, associated in particular, with the disposal of the now ubiquitous Li-ion batteries. There is, however, a paucity of information on the behaviour of Li in the soil-plant system. We measured the sorption of added Li to soil, and uptake of Li by food and fodder species. Around New Zealand, soil concentrations were shown to range from 0.08 mg/kg to 92 mg/kg, and to be positively correlated with clay content. Most geogenic Li in soil is insoluble and hence unavailable to plants but, when Li+ is added to soil, there is only limited sorption of Li. We found that Li sorption increased with increasing soil pH, and decreased proportionately with increasing Li concentrations. Compared to other cations in soil, Li is mobile and may leach into receiving waters, be taken up by plants, or have other biological impacts. In a soil spiked with just 5 mg/kg, plants took up several hundred mg/kg Li into leaves with no reduction in biomass. Lithium appears to be a phloem immobile element, with the highest concentrations occurring in the older leaves and the lowest concentrations occurring in the seeds or fruits. These results may raise concerns and risks in situations where food and fodder crops are associated with waste disposal.

Antimony retention and release from drained and waterlogged shooting range soil under field conditions.

Many soils polluted by antimony (Sb) are subject to fluctuating waterlogging conditions; yet, little is known about how these affect the mobility of this toxic element under field conditions. Here, we compared Sb leaching from a calcareous shooting range soil under drained and waterlogged conditions using four large outdoor lysimeters. After monitoring the leachate samples taken at bi-weekly intervals for >1.5 years under drained conditions, two of the lysimeters were subjected to waterlogging with a water table fluctuating according to natural rainfall water infiltration. Antimony leachate concentrations under drained conditions showed a strong seasonal fluctuation between 110 µg L(-1) in summer and <40 µg L(-1) in winter, which closely correlated with fluctuations in dissolved organic carbon (DOC) concentrations. With the development of anaerobic conditions upon waterlogging, Sb in leachate decreased to 2-5 µg L(-1) Sb and remained stable at this level. Antimony speciation measurements in soil solution indicated that this decrease in Sb(V) concentrations was attributable to the reduction of Sb(V) to Sb(III) and the stronger sorption affinity of the latter to iron (Fe) (hydr)oxide phases. Our results demonstrate the importance of considering seasonal and waterlogging effects in the assessment of the risks from Sb-contaminated sites.

Cadmium concentrations in new zealand pastures: relationships to soil and climate variables.

Cadmium (Cd) is a nonessential element that occurs at above-background concentrations in many New Zealand (NZ) soils. Most of this Cd is due to the historical application of single superphosphate that was made from Nauru phosphate rock containing between 400 and 600 mg Cd kg P. Pasture Cd uptake exacerbates the entry of Cd into animal products. We sought to determine the critical environmental factors affecting Cd uptake in NZ pastures and to calculate the likely Cd intake of sheep and cattle. We tested 69 pastures throughout NZ for a range of variables, including Cd. Soil Cd and pasture Cd were positively correlated with soil P and soil concentrations of other elements found in phosphate fertilizers. We found that no single environmental variable adequately predicted pasture Cd uptake. Nevertheless, pseudo-total soil Cd and Cd extracted using a 0.05 mol L Ca(NO) solution were positively correlated with pasture Cd. Although soil pH, soil Fe, and soil Cd provided an excellent predictor of the Ca(NO)-extractable soil Cd fraction, regression models explained just 38% of the variation of the Cd concentration in pasture grasses. Incorporating the effect of pasture species composition is a crucial next step in improving these models. A calculation of the likely exposure to Cd of sheep and cattle revealed that no pastures tested resulted in sheep and cattle ingesting Cd at a rate that would result in breaching muscle-tissue food standards. For offal products, which the NZ meat industry does not sell for human consumption, food safety standards exceedence was calculated in a few cases.

Lignite reduces the solubility and plant uptake of cadmium in pasturelands.

Repeated application of Cd-rich phosphate fertilizers can lead to the accumulation of this nonessential element in soil. This can result in increased plant uptake, with possible breaches of food or feed safety standards. We aimed to determine whether lignite (brown coal) can reduce Cd solubility and plant uptake in New Zealand pasture soils. In batch sorption experiments, we tested the capacity of lignite and lignite-soil mixtures to sorb Cd at various soil pH and Cd loadings. Over a pH range of 4-7, Cd sorption by lignite was 1-2 orders of magnitude greater than by a typic immature pallic soil containing 2% carbon. The addition of 5 wt % lignite to a range of soils revealed that lignite addition was most effective in reducing soluble Cd in soils with low pH. In a greenhouse experiment, we tested the effect of lignite on the accumulation of Cd and other elements by perennial ryegrass, Lolium perenne (L.). The addition of just 1 wt % lignite to the aforementioned soil reduced plant Cd uptake by 30%, without adversely affecting biomass or the uptake of essential nutrient elements including copper and zinc. This may be due to preferential binding of Cd to organic sulfur in lignite.