Kris Broos

White Clover Nodulation Index in Heavy Metal Contaminated Soils– A Potential Bioindicator

The morphological effects of heavy metal stress on the nodulation ability of Rhizobium spp. and growth of white clover (Trifolium repens L.) were studied in the laboratory under controlled conditions. Fourteen topsoils were collected from an area with elevated metal concentrations (Cd, Zn, and Pb). White clover was cultivated using a specialized rhizotron method to observe the development of root and nodule characteristics. Results show effects of increasing heavy metal concentrations on nodulation development, especially the nodulation index (i.e., the number of nodules per gram of the total fresh biomass). A significant decrease in nodulation index was observed at about 2.64 mg Cd kg(-1), 300 mg Zn kg(-1), and 130 mg Pb kg(-1) in these soils. The sensitivity of the nodulation index in relation to other morphological characteristics is discussed further. It is proposed that the nodulation index of white clover is a suitable bioindicator of increased heavy metal concentrations in soil.

Respiration and priming effects after fructose and alanine additions in two copper- and zinc-contaminated Australian soils

The objective of the present study was to determine whether substrate-induced priming effects in soils are sensitive to increasing levels of Cu and Zn. Soils were collected from ten plots of two Australian field experiments (Spalding and Avon) where increasing amounts of Cu or Zn had been added 2xa0years prior to sampling, reaching maximum values of 5,880xa0mgxa0kg−1 for Cu and 7,400xa0mgxa0kg−1 for Zn. In a 21-day incubation experiment, the effect of uniformly 14C-labeled fructose and alanine on the mineralization of the soil organic carbon (SOC) was investigated. With increasing heavy metal content, the initial peak of soil respiration after substrate addition was retarded, indicating that the microorganisms utilizing these substrates were inhibited in soils highly contaminated with heavy metals. Both substrates strongly changed the mineralization of the soil organic matter (SOM), i.e., priming effects were induced. In the soil samples with high Cu concentrations from Spalding, fructose induced a stronger additional mineralization of the SOC than in the lower contaminated samples. In the samples with the highest Zn contamination level, negative priming effects, i.e., a reduced mineralization of SOM, were observed. In contrast, heavy metal effects in the Avon soil (pHxa07.6) were less pronounced since substrate mineralization and priming effects were not directly related to the increasing heavy metal content. Apart from direct toxic heavy metal effects, the tested microbial activity parameters were also indirectly affected through the toxic heavy metal effects on plant growth. At the highest heavy metal contaminations, no fresh biomass inputs occurred during the past 2xa0years so that microorganisms in these soils were highly substrate-limited. As a consequence, complex interactions between different levels of heavy metal contamination, the microbial activity, and the input of SOC via plant biomass have to be considered.

Round robin testing of a percolation column leaching procedure

Round robin test results of a percolation column leaching procedure (CEN/TS 14405:2004), organised by the Flemish Institute for Technological Research (VITO), over a time span of 13years with a participation of between 8 and 18 different laboratories are presented and discussed. Focus is on the leachability of heavy metals As, Cd, Cr, Cu, Hg, Ni, Pb and Zn from mineral waste materials. By performing statistical analyses on the obtained results, insight into the reproducibility and repeatability of the column leaching test is gathered. A ratio of 1:3 between intra- and inter-laboratory variability is found. The reproducibility of the eluates element concentrations differ significantly between elements, materials and fractions (i.e. different liquid-to-solid ratios). The reproducibility is discussed in light of the application of the column leaching test for legal and environmental policy purposes. In addition, the performances of laboratories are compared.

Closed-loop solvometallurgical process for recovery of lead from iron-rich secondary lead smelter residues

A solvometallurgical process based on the use of concentrated acetic acid as lixiviant is proposed as an alternative for conventional hydrometallurgical processes to recover lead from iron-rich industrial residues generated by recycling of spent lead-acid batteries in a secondary lead smelter. Under the optimal conditions, a high selectivity for lead was obtained: more than 90% of the lead content could be dissolved, while only a small amount of iron (<6%) was codissolved. Lead was quantitatively recovered from the acetic acid leachate by addition of a stoichiometric amount of sulphuric acid. Acetic acid was recycled by distillation and reused in the leaching step, so that a closed-loop process was obtained. The process was optimised for iron-rich residue (matte), but also a proof-of-principle is given for lead recovery from another lead-containing residue (slag). The main advantages of this solvometallurgical process are the low power consumption (room-temperature process), the low consumption of chemicals (only sulphuric acid is consumed), full recycling of the acetic acid and the limitation of waste water formation.