Hydrogel determined metal bioaccessibility in acid sulfate-affected landscapes

Exposure of sulfidic sediments to atmospheric conditions can under various environmental and anthropogenic influences. The oxidation of sulfides results in the production of acidity, dissolution of aluminosilicates and pedogenci development. This process has acid sulfate landscapes throughout the world identified as major emitters of elevated concentrations of chemical metals. This emission of acidity and metals alters the bioaccessibility and subsequently has a deleterious impact on the surrounding biologic environment. Despite this, the examination of the biologic impact in these landscapes has received only minimal attention. Passive and dynamic hydrogel techniques were used to measure the bioaccessibility of metals in sediments and waters. The technique involved the construction of a restricted pore-size thin-film hydrogel that allowed for the diffusion of the bioaccessible fraction, composed of the free-ion and easily dissociable metal-complexes. The dynamic hydrogel technique contained a resin sink, which allowed for a time-integrated flux concentration to be calculated. The dynamic hydrogel technique was trialled and found to correlate with the pygmy mussel (Xenostrobus securis) aluminium uptake for short exposure periods (24 hours).The dynamic hydrogel metal concentration was also found to correlate to indpendantly measured pore water and simultaneously extracted metal (SEM) concentrations.The hydrogel techniqe was further applied to investigate the sediment-water interface in drained and non-drained acid suflate landscapes. The studied Australian and Finnish acid sulfate landscapes showed contrasting relationships between the acid volatile sulfides (AVS) and SEM fractions. In the Australian sediments, a conversion of AVS-S to FeS2-S occurs with depth driven by a polysulfide pathway, whilst the Finnish sediments displayed a persistence of AVS-S with depth with limited conversion to FeS2-S. Distinct variations exist at the sediment-water interface of the two contrasting landscapes, with AVS-S to FeS2-S ratios of 2.5 for the Australian and 0.2 in the Finnish sediments. The sediment geochemistry regulated metal mobility. A two-dimensional passive and dynamic hydrogel approach illustrated microniches and supply zones of aluminium iron, manganese and zinc at varying depths near the sediment-water interface. The measurement of bioaccessibility using an in situ technique in acid sulfate landscapes is a first for both Australia and Finland, and this research provides an important avenue for future water and sediment quality monitoring