Cadmium Background Levels in Groundwater in an Area Dominated by Agriculture.

Cadmium is a highly toxic trace metal, which can be of geogenic or anthropogenic origin, for example, minerals, phosphate fertilizers, and combustion emissions. Due to its low sorption affinity compared to other heavy metals, Cd is easily mobilized, potentially resulting in elevated Cd concentrations in groundwater. This study assessed background levels of Cd in groundwater related to hydrogeology and hydrogeochemical processes through evaluation of a large hydrogeochemical data set composed of groundwater analyses from 6300 wells in Northwestern Germany. Calculated Cd background levels in groundwater were between 0.01 µg/L in hydrogeological units with mainly reducing conditions and 0.98 µg/L in less reducing groundwater recharge areas. The results showed that groundwater Cd concentrations above 0.5 µg/L (the German threshold value) are not necessarily elevated but could be the regional or ambient background level, depending on the hydrogeological unit. What would be considered as ambient background levels, however, indicated the influence by continuous intensive land use as well as the local geology, which is dominated by glacial deposits. Cadmium concentrations in groundwater were mainly controlled by hydrogeochemical and hydrogeological parameters and not by the amount of anthropogenic Cd input, in particular through the use of phosphate fertilizers. Instead, analyses of the solid phase revealed that Cd release from the aquifer matrix due to changes in hydrogeochemical parameters was more likely. Aquifer sediments in Northwestern Germany can be enriched in Cd originating from multiple sources, which in turn can cause elevated Cd concentrations in groundwater. Integr Environ Assess Manag 2019;00:1-11. © 2019 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Tributyltin release from harbour sediments--modelling the influence of sedimentation, bio-irrigation and diffusion using data from Bremerhaven.

This study describes the potential release of TBT from harbour sediments based on model calculations for different sediment management scenarios applying a numerical one-dimensional FD-model. A conceptual model was developed focussing on the following processes involved in the transport of TBT: sorption equilibrium, diffusion, irrigation and sedimentation. Assuming TBT-concentration of 292 microg/kg in the sediment, the diffusive release of TBT from sediments into the bottom water was calculated to 7.4 x 10(-7)-6.9 x 10(-6)mol m(-2) after 1 year and 7.4 x 10(-6)-1.6 x 10(-4)mol m(-2) after 100 years. In these scenarios, neither sedimentation nor capping were considered. Assuming a sedimentation at a rate of 1cm/a, the polluted sediments will be covered with TBT-free suspended matter. A diffusive release of TBT will be prevented if no bio-irrigation takes place. Capping with a layer of sand of 50 cm thickness will decrease the diffusive release. If a reactive capping could be applied, the release of TBT into the bottom water would be stopped almost completely. The study shows that our model calculations enables us to compare different scenarios in sediment management based on available data. Additionally, it can provide information for risk assessment in the absence of data.

Reaction fronts in brick-sand layers: column experiments and modeling.

Admixing waste materials with common raw materials in brick production is a promising treatment technology to overcome contamination problems, because organic pollutants are destroyed and inorganic contaminants are thought to be immobilized. During their use in constructions and after the use as part of the demolition masses bricks can be leached by runoff waters and seepage waters. A possible application of recycling crushed bricks consists of their use as a surface layer material on sports grounds or in road construction. To investigate the potential leaching during acidification of a brick-sand layer and the resultant leaching of heavy metals, crushed material from two bricks was examined in several column experiments. Deionized water at pH 4 percolated through the water-saturated columns at a Darcy velocity which was varied between 0.37 and 2.2 m/d. Another column was run under unsaturated conditions. A reaction front evolved in all experiments characterized by a pH increase from pH 4 to pH 8. The chemical composition of the percolating water changed at the reaction front. Several heavy metals (Cd, Co, Cu, Ni) and Al were immobilized at this front. Other parameters such as Ca, S as SO4, V, and Mo were depleted within several days. The reaction front moved forward depending on the Darcy velocity in the column and the buffer capacity of the brick sand. Thermodynamic calculations (PHREEQC 2.0) indicated that mobilization of As was influenced by Ba(AsO4)2. The solubility of Ba and Mn was controlled by barite and manganite, respectively. Reactive transport modeling was applied to describe the dissolution of the bricks with regard to their main components Ca, SO4, Al, and Si.

Brick production with dredged harbour sediments. An industrial-scale experiment.

A volume of 600.000 m3 harbour sediments is annually dredged out of the harbour basin of Bremen to maintain a certain water depth. Because of its perpetual availability, homogeneity and mineralogical, petrographic and chemical composition, the sediment is regarded as a suitable raw material for brick production. A pilot experiment was conducted at a full-scale industrial brickworks. During production, the environmental standards concerning waste-water treatment and the quality of exhausted gas were sufficiently fulfilled. Bricks specified as "building bricks" were produced according to German industrial standards. The parameters pH-value and grain size were varied in leaching tests performed on the bricks as both parameters are likely to change in the course of the brick's life cycle. The leaching data showed that As was stabilised and heavy metals were immobilised in a way that the bricks were not (hazardous to soil or groundwater) neither by their use, for example, in masonry, nor afterwards, when they will be deposited as mineral demolition mass.