Environmental context. Potassium is an essential plant nutrient and farmers need to be able to predict how much soil K is plant available in order to optimise fertiliser applications and crop production. Traditional methods such as chemical extraction are generally poor predictors. A DGT based methodology that could enhance the assessment of plant available K is developed, which will assist plant growers to determine the correct fertiliser application, thereby avoiding crop deficiencies and limiting the misuse of K as a precious natural resource.

Environmental context. Metal species can have significant toxic effects in aquatic systems, and therefore their occurrence should be reliably monitored. Although many methods to measure metal species are available, they all have limitations and are sensitive to physicochemical complications. It is shown that, in techniques based on diffusive gradients in thin films, sorption of humic acids affects metal speciation inside the diffusive gel layer and the nature of the ensuing flux response.

Environmental context. Contamination of aquatic ecosystems with inorganic arsenic is a concern for both environmental and human health. Sediments are an important sink for dissolved arsenic, but they may also act as a source of arsenic because of human-induced changes in aquatic systems. This paper describes a new approach for investigating the status of inorganic arsenic in sediments, based on recent developments in diffusion-based sediment sampling techniques.

Environmental context. Contaminated sediments can have a large and lasting effect on marine ecosystems. It was discovered that significant amounts of pollutants, especially arsenic, were released from contaminated sediments during a phytoplankton bloom in the Belgian Continental Zone. Once released to the water column, these pollutants can accumulate up marine food chains and be a source of contaminants to humans.

Environmental context. Uptake of metal ions by plants is often predicted with equilibrium models, which assume that the rate limiting step is trans-membrane uptake of the metal in the roots rather than the transport of the metal ion towards the site of uptake. Evidence is given that uptake of cadmium by plants is under strong transport control at environmentally relevant concentrations, whereas nickel uptake borders between transport and plant control. This explains the lack of ion competition effects for Cd uptake, whereas both proton and Mg ions were found to compete with Ni uptake.

Environmental context. Both the mobility and toxicity of arsenic in natural waters are related to the aqueous species distribution. Passive sampling using ferrihydrite-backed diffusive gradients in thin films (DGT) devices has in previous studies been characterised to measure labile inorganic arsenic, and the possible contribution of organic species has been disregarded. This study shows that the two most prevalent organic arsenic species might be included in DGT measurements, which should be taken into consideration when evaluating DGT data in future studies.

Environmental context. In urban environments such as parks and gardens, polluted soils can have a direct influence on children’s health. This study investigates Pb, Cu and Zn concentrations in soils of several public parks in Rome city (Italy) located near roads with high traffic loads. It is shown that vehicle traffic contributes significantly to soil metal pollution in the urban parks and gardens, and that barriers such as walls and trees reduce the metal accumulation.

Environmental context. Although arsenic occurs at high concentrations in many marine systems, the influencing factors are poorly understood. The arsenic content of sediments, detritus, suspended particles and organisms have been investigated from different trophic levels in an open seagrass ecosystem. Total arsenic concentrations and arsenic species were organism-specific and determined by a variety of factors including exposure, diet and the organism physiology.

Environmental context. In terrestrial environments, humic substances act as major sorbents for calcium, which is an essential nutrient for organisms. This study shows that calcium binding by terrestrial humic acids is strongly dependent on pH and ionic strength. The results indicate that calcium binding by humic acids is primarily controlled by electrostatic forces and specific binding to carboxylic groups.

Environmental context. The association of specific organic matter (OM) compounds with clay mineral surfaces is believed to protect these compounds from degradation and thus result in long-term protection in soil. The molecular-level composition of soil OM associated with soil fractions was measured and compared using solid-state ¹³C nuclear magnetic resonance (NMR) and solution-state ¹H NMR methods. Combining these methods allowed more detailed characterisation of OM associated with different soil fractions and will improve the understanding of OM dynamics in soil.