Land disposal of treated human and animal effluent through pumice sand soils is a common practice around Rotorua, in the central North Island of New Zealand. There is increasing concern about the possibility of contamination of shallow pumice sand aquifers associated with this practice. In this study, we investigated the transport and attenuation of F-RNA bacteriophages and Escherichia coli in saturated pumice sand aquifer media using a field tracing experiment, and laboratory batch and column studies. The influence of dissolved organic carbon on microbial transport was also investigated by conditioning the 18 cm-long column with ultrafiltered sewage. The CXTFIT curve-fitting program was used to model the experimental data and to determine transport and attenuation parameters. Batch studies showed more than 90% adsorption of both microbial indicators onto pumice sand. High mass removal of microbial indicators was shown in the field (>99% for phage MS2 and E. coli at 2 m down gradient of the injection well; not detected at 6 m) and in the 'clean sand' column (65% for phage MS2 and 90% or E. coli). These results suggest that uncontaminated pumice is an effective sorbent capable of retaining microbial contaminants due to high surface area and porosity. However, in the column, with additional dissolved organic carbon, phages showed a progressive reduction in mass removal and retardation between experiments (93%, 75%, and 63% removal; retardation factor: 3.5, 2.5 and 1.2). This suggests that the organic matter competed with phages for the sorption sites, thus promoting phage transport. As a result, viral transport rates may be significantly greater in contaminated compared with uncontaminated pumice sand aquifers.

A 20-month column experiment investigated leaching of Al, Cu, Mn, Ni, Zn, Cd and Pb during sulphide oxidation in mine tailings with and without sewage sludge (SS) amendment. Leachate pH decreased gradually in all columns during the experiment, irrespective of treatment, due to sulphide oxidation. As the degree of sulphide oxidation, and thus the pH trajectory, differed between replicates (n = 3), running data for each column used are reported separately and the relationships between sulphide oxidation, metal leaching and treatment in each column compared. Mean pH in the columns correlated negatively with total amounts of leached SO₄ ²⁻. In the beginning of the experiment the leachate concentrations of Al, Cu, Zn, Ni and Pb were higher in SS-treated columns due to high initial concentrations of dissolved organic carbon. As leaching proceeded, however, the amounts of Al, Cu, Mn and Ni leached from the columns were closely related to the degree of sulphide oxidation in each column, i.e. to its mean pH. There were no statistically significant differences between treatments regarding the total amounts of metals leached and thus addition of sewage sludge to the tailings appeared to play a minor role for metal leaching patterns. Peak concentrations of Al and Cu in the leachate from untreated tailings and of Zn in the leachate from both untreated and SS-treated tailings at pH 4 exceeded national background values for groundwater.

Mercury and organic carbon concentrations vary dynamically in streamwater at the Sleepers River Research Watershed in Vermont, USA. Total mercury (THg) concentrations ranged from 0.53 to 93.8 ng/L during a 3-year period of study. The highest mercury (Hg) concentrations occurred slightly before peak flows and were associated with the highest organic carbon (OC) concentrations. Dissolved Hg (DHg) was the dominant form in the upland catchments; particulate Hg (PHg) dominated in the lowland catchments. The concentration of hydrophobic acid (HPOA), the major component of dissolved organic carbon (DOC), explained 41-98% of the variability of DHg concentration while DOC flux explained 68-85% of the variability in DHg flux, indicating both quality and quantity of the DOC substantially influenced the transport and fate of DHg. Particulate organic carbon (POC) concentrations explained 50% of the PHg variability, indicating that POC is an important transport mechanism for PHg. Despite available sources of DHg and wetlands in the upland catchments, dissolved methylmercury (DmeHg) concentrations in streamwaters were below detection limit (0.04 ng/L). PHg and particulate methylmercury (PmeHg) had a strong positive correlation (r ² = 0.84, p < 0.0001), suggesting a common source; likely in-stream or near-stream POC eroded or re-suspended during spring snowmelt and summer storms. Ratios of PmeHg to THg were low and fairly constant despite an apparent higher methylmercury (meHg) production potential in the summer. Methylmercury production in soils and stream sediments was below detection during snowmelt in April and highest in stream sediments (compared to forest and wetland soils) sampled in July. Using the watershed approach, the correlation of the percent of wetland cover to TmeHg concentrations in streamwater indicates that poorly drained wetland soils are a source of meHg and the relatively high concentrations found in stream surface sediments in July indicate these zones are a meHg sink.

Interdisciplinary studies on aquatic environments and cross-validation of laboratory vs. field results will likely increase the need for simultaneous use of large- and small-scale ultrafiltration systems. In this study, a comparison of two ultrafiltration systems differing in scale (PrepScale and PelliconXL, Millipore; membrane areas 0.54 m² and 0.005 m², respectively), was made for the cut-offs 3 and 300 kDa. Large systems are useful for their high permeate throughput, while small systems are necessary when the amount of sample is limited. The ability of PrepScale and PelliconXL systems to provide comparable results for organic carbon fractionation was studied for polysaccharide solutions and natural freshwaters. In the latter, the colloidal proportions of different trace metals (V, Cr, Mn, Co, Ni, Cu, Sb, and U) were also determined. Although the colloidal proportions obtained with PelliconXL 3 kDa were sometimes slightly higher than with PrepScale 3 kDa (principally for DOC and U in natural waters), Mann-Whitney statistical test showed no significant difference in the overall fractionation properties of the two systems. Our observations show that reaching high concentration factors lead to a strong modification of colloids size distribution in the range 50-2,000 nm and thus low concentration factors are preferable to preserve the colloid integrity.

The mobility of mercury (Hg) deposited on soils controls the concentration and toxicity of Hg within soils and in nearby streams and lakes, but has rarely been quantified under field conditions. We studied the in situ partitioning of Hg in the organic top layer (mor) of podsols at two boreal forest sites differing in Hg deposition and climatic regime (S. and N. Sweden, with pollution declining to the north). Soil solution leaching from the mor layer was repeatedly sampled using zero-tension lysimeters over 2 years, partly in parallel with tension lysimeters. Concentrations of Hg and dissolved organic carbon (DOC) were higher while pH was lower at the southern site (means ± SD: Hg = 44 ± 15 ng L-¹, DOC = 63.0 ± 31.3 mg L-¹, pH = 4.05 ± 0.53) than at the northern site (Hg = 22 ± 6 ng L-¹, DOC = 41.8 ± 12.1 mg L-¹, pH = 4.28 ± 0.43). There was a positive correlation over time between dissolved Hg and DOC at both sites, even though the DOC concentration peaked during autumn at both sites, while the Hg concentration remained more constant. This correlation is consistent with the expected strong association of Hg with organic matter and supports the use of Hg/C ratios in assessments of Hg mobility. In the solid phase of the overlying Of layer, both Hg concentrations and Hg/C ratios were higher at the southern site (means ± SD: 0.34 ± 0.06 μg g-¹ dw and 0.76 ± 0.14 μg g-¹ C, respectively) than at the northern site (0.31 ± 0.05 μg g-¹ dw and 0.70 ± 0.12 μg g-¹ C, respectively). However, concentrations in the solid phase differed less than might be expected from the difference in current atmospheric input, suggesting that the fraction of natural Hg is still substantial. At both sites, Hg/C ratios in the upper half of the mor layer were only about two thirds of those in the lower half, suggesting that the recent decrease in anthropogenic Hg deposition onto the soil is offset by a natural downward enrichment of Hg due to soil decomposition or other processes. Most interestingly, comparison with soil leachate showed that the average Hg/C ratios in the dissolved phase of the mor layers at both sites did not differ from the average Hg/C ratios in the overlying solid organic matter. These results indicate a simple mobilisation with negligible fractionation, despite differences in Hg deposition patterns, soil chemistry and climatic regimes. Such a straight-forward linkage between Hg and organic matter greatly facilitates the parameterisation of watershed models for assessing the biogeochemical fate, toxic effect and critical level of atmospheric Hg input to forest soils.