Proposal to optimize ecotoxicological evaluation of wastewater treated by conventional biological and ozonation processes

A mixture of urban and hospital effluents (50 % v/v) was evaluated for ecotoxicity with an advanced bioassay battery. Mixed effluents were tested before any treatment, after biological treatment alone, and after biological treatment followed by a tertiary ozonation (15 mg O₃/L). Laying a high value on the continuance of organisms’ fitness, essential to preserve a healthy receiving ecosystem, the main objective of this study was to combine normalized bioassays with newly developed in vivo and in vitro tests in order to assess alteration of embryo development, growth and reproduction, as well as genotoxic effects in aquatic organisms exposed to complex wastewater effluents. Comparison of the bioassays sensitivity was considered. Contrary to the lack of toxicity observed with normalized ecotoxicity tests, endpoints measured on zebrafish embryos such as developmental abnormalities and genotoxicity demonstrated a residual toxicity in wastewater both after a biological treatment followed or not by a tertiary O₃ treatment. However, the ozonation step allowed to alleviate the residual endocrine disrupting potential measure in the biologically treated effluent. This study shows that normalized bioassays are not sensitive enough for the ecotoxicological evaluation of wastewaters and that there is a great need for the development of suitable sensitive bioassays in order to characterize properly the possible residual toxicity of treated effluents.     

One step forward toward characterization: some important material properties to distinguish biochars

Terra Preta research gave evidence for the positive influence of charred organic material (biochar) on infertile tropical soils. Facing global challenges such as land degradation, fossil energy decline, water shortage, and climate change, the use of biochar as a soil amendment embedded into regional matter cycles seems to provide an all-round solution. However, little is known about biochar effects on individual ecosystem processes. Besides, the term is used for a variety of charred products. Therefore, the aim of this study was to investigate principal material properties of different chars to establish a minimum set of analytical properties and thresholds for biochar identification. For this purpose, chars from different production processes (traditional charcoal stack, rotary kiln, Pyreg reactor, wood gasifier, and hydrothermal carbonization) were analyzed for physical and chemical properties such as surface area, black carbon, polycyclic aromatic hydrocarbons, and elemental composition. Our results showed a significant influence of production processes on biochar properties. Based on our results, to identify biochar suitable for soil amendment and carbon sequestration, we recommend using variables with the following thresholds: O/C ratio <0.4, H/C ratio <0.6, black carbon >15% C, polyaromatic hydrocarbons lower than soil background values, and a surface area >100 m g.     

Exposure assessment of French women and their newborn to brominated flame retardants: determination of tri- to deca- polybromodiphenylethers (PBDE) in maternal adipose tissue, serum, breast milk and cord serum

In the frame of a French monitoring program, tri- to deca- polybromodiphenylethers (PBDE) have been measured in maternal and cord serum, adipose tissue, and breast milk samples, collected from 93 volunteer women during caesarean deliveries. The seven major tri- to heptaBDE (BDE-28, 47, 99, 100, 153, 154, and 183) were detected in adipose tissue and breast milk with cumulated median values of 2.59 and 2.51 ng g⁻¹ l w. Nine highly brominated octa- to decaBDE (BDE-196, 197, 201, 202, 203, 206, 207, 208 and 209) was performed in the same samples, with cumulated median values of 2.73 and 3.39 ng g⁻¹ l w in adipose tissue and breast milk, respectively. At this opposite, median levels of octa- to decaBDE in maternal and cord serum appeared significantly higher than the levels of tri- to heptaBDE in the same matrices, i.e. 8.85 and 12.34 versus 0.98 and 0.69 ng g⁻¹ l w, respectively.     

Do wood mice (Apodemus sylvaticus L.) use food selection as a means to reduce heavy metal intake?

Food preference of wood mice from two with heavy metals polluted sites and two unpolluted sites was tested under laboratory and field conditions with two-way choice experiments. In the laboratory, wood mice preferred to eat acorns from unpolluted sites over acorns from polluted sites. Previous experience with polluted food had no influence on food choice. Preference was negatively related to acorn metal content. Furthermore, the nutrient content of the acorn endosperm was consistently lower in polluted sites. We therefore conclude that wood mice used absolute metal concentration in the acorn, nutrient content, or both as a food selection cue. The results of the laboratory experiment could not be confirmed under field conditions. We hypothesized that search time constraints due to the presence of predators, competitors and/or other stress factors in the field have prevented the mice to forage selectively.     

Passive treatment of acid mine drainage in bioreactors using sulfate-reducing bacteria: critical review and research needs

Acid mine drainage (AMD), characterized by low pH and high concentrations of sulfate and heavy metals, is an important and widespread environmental problem related to the mining industry. Sulfate-reducing passive bioreactors have received much attention lately as promising biotechnologies for AMD treatment. They offer advantages such as high metal removal at low pH, stable sludge, very low operation costs, and minimal energy consumption. Sulfide precipitation is the desired mechanism of contaminant removal; however, many mechanisms including adsorption and precipitation of metal carbonates and hydroxides occur in passive bioreactors. The efficiency of sulfate-reducing passive bioreactors is sometimes limited because they rely on the activity of an anaerobic microflora [including sulfate-reducing bacteria (SRB)] which is controlled primarily by the reactive mixture composition. The most important mixture component is the organic carbon source. The performance of field bioreactors can also be limited by AMD load and metal toxicity. Several studies conducted to find the best mixture of natural organic substrates for SRB are reviewed. Moreover, critical parameters for design and long-term operation are discussed. Additional work needs to be done to properly assess the long-term efficiency of reactive mixtures and the metal removal mechanisms. Furthermore, metal speciation and ecotoxicological assessment of treated effluent from on-site passive bioreactors have yet to be performed.     

Fractional calculus applied to the analysis of spectral electrical conductivity of clay-water system

The analysis of the low-frequency conductivity spectra of the clay-water mixtures is presented. The frequency dependence of the conductivity is shown to follow the power-law with the exponent n=0.67 before reaching the frequency-independent part. When scaled with the value of the frequency-independent part of the spectrum the conductivity spectra for samples at different water content values are shown to fit to a single master curve. It is argued that the observed conductivity dispersion is a consequence of the anomalously diffusing ions in the clay-water system. The fractional Langevin equation is then used to describe the stochastic dynamics of the single ion. The results indicate that the experimentally observed dielectric properties originate in anomalous ion transport in clay-water system characterized with time-dependent diffusion coefficient.     

Trace metal dynamics in an industrialized Brazilian river: A combined application of Zn isotopes, geochemical partitioning, and multivariate statistics

The Paraiba do Sul (PSR) and Guandu Rivers (GR) water diversion system (120 km long) is located in the main industrial pole of Brazil and supplies drinking water for 9.4 million people in the metropolitan region of Rio de Janeiro. This study aims to discern the trace metals dynamics in this complex aquatic system. We used a combined approach of geochemical tools such as geochemical partitioning, Zn isotopes signatures, and multivariate statistics. Zinc and Pb concentrations in Suspended Particulate Matter (SPM) and sediments were considerably higher in some sites. The sediment partition of As, Cr, and Cu revealed the residual fraction (F4) as the main fraction for these elements, indicating low mobility. Zinc and Pb were mostly associated with the exchangeable/carbonate (F1) and the reducible (F2) fractions, respectively, implying a higher susceptibility of these elements to being released from sediments. Zinc isotopic compositions of sediments and SPM fell in a binary mixing source process between lithogenic (δ^66/64Zn_JMC ≈ + 0.30‰) and anthropogenic (δ^66/64Zn_JMC ≈ + 0.15‰) end members. The lighter δ^66/64Zn_JMC values accompanied by high Zn concentrations in exchangeable/carbonate fraction (ZnF1) enable the tracking of Zn anthropogenic sources in the studied rivers. Overall, the results indicated that Hg, Pb, and Zn had a dominant anthropogenic origin linked to the industrial activities, while As, Cr, and Cu were mainly associated with lithogenic sources. This work demonstrates how integrating geochemical tools is valuable for assessing geochemical processes and mixing source effects in anthropized river watersheds.     

Heavy metal and polycyclic aromatic hydrocarbons in Ebrié lagoon sediments, Côte d’Ivoire

Surface sediments throughout Ebrié lagoon, Côte d’Ivoire were collected in 2001 and analyzed for their heavy metal and polycyclic aromatic hydrocarbons (PAH) contaminant content. Geochemical maps of heavy metals (Cd, Cu, Zn, Fe, and Mn) in the surface sediment were produced based on geographical information system (GIS) technology. Heavy metals and PAH were detected at high concentration and provide evidence for several anthropogenic inputs to the lagoon. A significant spatial relationship was found for Fe, Zn, and Cu in the sediment using a GIS-based analysis, suggesting that these metal contaminants in the sediments of the Biétri bay had common sources.