Since the last century, humanity has sought ways to minimize the impact of the industrial growth in the environment. The textile industry, as one of the major contributors to water pollution, has been dumping coloured effluents which cause great impact in water bodies. The electrolytic process not only degrades the colour of the effluent but also transforms recalcitrant substances by direct or indirect oxidation. The ecotoxicological tests are used nowadays as a way to verify the toxicity degree of water bodies polluted by industrial and farming activities. The ecotoxicological tests consist in exposing determined organisms to the samples with the intention to evaluate their toxicity by observing the organisms’ responses. This study had the objective to degrade, by electrolytic process, a simulated textile effluent containing a mixture of Acid Blue 40 and Acid Red 151 dyes and the toxicity evaluation of the treated effluent by ecotoxicological tests. The bioassays used were tests with seeds of Lactuca sativa (lettuce), Eruca sativa (rocket), and Cucumis sativus (cucumber). Tests with the micro crustaceous Artemia salina and the yeast Saccharomyces cerevisiae were also conducted. The electrolytic treatment degraded the initial colour of the textile effluent, and the ecotoxicological tests indicated low toxicity to the treatment.

The degradation of hexachlorobenzene (HCB) is of great concern and attracts considerable scientific and regulatory interests, due to the high toxicity, great bioaccumulation, and persistence of HCB in the environment. However, in the real HCB-contaminated soil, the effect of coexisting chlorobenzene congeners on the degradation capacity of HCB is poorly known. In this work, the anaerobic degradation behaviors of three coexisting chlorobenzene congeners pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), and 1,2,4-trichlorobenzene (1,2,4-TCB) and the influence of initial pH and reaction temperature on the dechlorination of HCB in HCB-contaminated soil from the dye plant were studied. The amount and extent of accumulated coexisting chlorobenzenes was analyzed under different environmental conditions. The results indicate that the concentrations of three coexisting chlorobenzene congeners change in the form of wave. The anaerobic degradation activity of HCB is reduced due to the feedback inhibition caused by accumulation of coexisting chlorobenzene congeners, and the feedback inhibition varies from environmental conditions.

Chemical methods have been used for the remediation of arsenic (As)-contaminated water; however, ecological consequences of these methods have not been properly addressed. The present study evaluated the effects of the Fe-oxide-coated sand (IOCS) remediation method on As toxicity to freshwater organisms (Lemna disperma, Chlorella sp. CE-35, and Ceriodaphnia cf. dubia). The As removal efficiency by IOCS decreased substantially with time. The IOCS remediation method was less effective at suppressing the toxicity of Asⱽ than Asᴵᴵᴵ to L. disperma but was highly effective in reducing both the Asᴵᴵᴵ and Asⱽ toxicity to C. cf. dubia. The growth of Chlorella sp. was significantly higher (p < 0.05) in remediated and pre-remediated water than in controls (non-As-contaminated filtered Colo River water) for Asᴵᴵᴵ, while the opposite was observed for Asⱽ, indicating that Asⱽ is more toxic than Asᴵᴵᴵ to this microalga. Although the IOCS can efficiently remove As from contaminated water, residual As and other constituents (e.g. Fe, nitrate) in the remediated water had a significant effect on freshwater organisms.

Nutrient enrichment is considered one of the most important causes for summer hypoxic conditions in the northern Gulf of Mexico (NGOM) off the Louisiana coast. While many studies on nutrient inputs from the large Mississippi-Atchafalaya River System have been conducted, little is known about nutrient inputs from other coastal rivers in Louisiana. In this study, we utilized long-term (1980–2009) records on river discharge and nutrient concentrations of four major Louisiana coastal rivers—the Sabine, Calcasieu, Mermentau, and Vermilion—to estimate daily, monthly, and annual inflows of nitrate and nitrite nitrogen (NO₃ + NO₂), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) into the NGOM. The three-decade-long nutrient inflows from these rivers were analyzed for their seasonal fluctuations, interannual variabilities, and decadal trends. Fluxes of NO₃ + NO₂, TKN, and TP for these river basins were estimated to assess land use effects on riverine nutrients. Our study found that the four coastal rivers discharged each year a considerably large amount of NO₃ + NO₂ (total of 1755 t), TKN (12,208 t), and TP (1833 t) into the NGOM, with a peak input of nitrogen during the spring. The Mermentau and Vermilion Rivers, which drain intensive agriculture areas, had significantly higher NO₃ + NO₂, TKN, and TP concentrations when compared with the Sabine and Calcasieu Rivers, which drain forest-pasture-dominated lands. The fluxes of NO₃ + NO₂, TKN, and TP from the Mermentau River Basin (156 kg km⁻² year⁻¹ NO₃ + NO₂, 942 kg km⁻² year⁻¹ TKN, and 206 kg km⁻² year⁻¹ TP) and the Vermilion River Basin (374, 1078, and 360) were much higher than those combined from the Sabine and Calcasieu River Basins (66, 710, and 62). These findings fill a major knowledge gap concerning the quantity and characteristics of nitrogen and phosphorus transport from coastal watersheds to North America’s largest hypoxic zone.

Copper bioavailability, specially to plants, is strongly dependent on its chemical form, as for most metals. Copper-contaminated soil can be treated in situ by the addition of minerals such as Na-bentonite, which mixed with surface soil, can transform this pollutant to non-bioavailable forms. In this work, shelter experiments were conducted to study the time evolution of Cu speciation, in pristine soil as well as in amended one. A selective sequential extraction method was employed to determine the metal speciation in the samples. The results show that the major metal fraction is the organic matter-bound one, whereas the exchangeable fraction is very low, even the first day after Cu addition. The time evolution shows a slow decrease of the organic-bound Cu and a corresponding increase of the most stable mineral fractions. With the addition of Na-bentonite to copper-contaminated soil, the most stable mineral fractions increase whereas the organic-bound one decreases, showing essentially similar time dependence of the several metal fractions. Sodium bentonite could be effectively used for remediation of soils polluted with Cu.

We report on treatment and disposal of flue gas desulfurization (FGD) as a solid and hazardous waste. The effects of modified flue gas desulfurization residue (MFGDR) prepared by calcining a mixture of dry/semi-dry FGD residue, potassium feldspar, and/or limestone power on growth of plant and soil amelioration are investigated. The effect of MFGDR on the sweet potato was evaluated by analyzing the soil physiochemical properties and heavy metal speciation in the soil, and the yield, quality, and heavy metal concentrations of the sweet potato. The results indicated that applying MFGDR as soil ameliorant increased total yield by 53.38 %, safety, and the quality of sweet potato. The concentrations of Cd, Cr, Cu, Pb, and As in the sweet potato reduced by 31.34, 70.57, 22.17, 79.49, and 100 %, respectively. The improvements were attributed to enhancement of soil mineral composition contained in MFGDR. The MFGDR could also improve the soil physicochemical properties and decreased phytoavailability of heavy metals. The application of MFGDR in agriculture not only was a potential and useful technique for recycling and utilization of FGD residue, but also had potential benefits for soil amelioration, plant growth, and decrease of heavy metals in grown products.

Eutrophication is a main cause for impairment of freshwater ecosystems, and diffuse phosphorus (P) loss from agricultural land is usually the main cause for freshwater eutrophication. The P index is a simple and practical tool for estimating the potential P loss risk. In a preceding study, a refined P index scheme was developed and validated. In the current study, the relative importance of the 14 input variables used is assessed in order to determine their relative significance to the final P index value. The backpropagation network with Garson’s algorithm was employed in order to capture the significance of interactions among the input variables. The study clearly shows the source factors, especially the degree of P saturation (DPS), along with management practices regarding application of inorganic P fertilizer and livestock manure, are the most important factors governing the P loss in the very high and high risk areas. Conversely, the transportation factors governed P loss risk in the low and very low risk areas. Recommended management strategies for mitigation of P loss from the different risk zones are proposed based on the relative importance analysis and practical constraints. A scenario analysis, based on a gradient reduction of DPS, through decreased application of both inorganic P fertilizer and P emissions factors from livestock manure, gave a reduction of average P index from 7.3 to 57 %. Moreover, the proportion of high- and very-high-risk area may be reduced from 38 to 23 % and 24 to 13 %, respectively.

In this study, various metal concentrations were determined in environmental samples from rivers in the vicinity of mining areas of the Northwest Province, South Africa. These metal concentrations were also determined in various crustacean organs viz., hepatopancreas, flesh and muscle of the freshwater crab, Potamonautes warreni. The highest metal concentrations obtained in the freshwater samples were Ni (0.022 mg/l), Pb (0.02 mg/l), Cu (0.011 mg/l), Cd (0.009 mg/l), Pt (0.017 μg/l), Pd (0.011 μg/l) and Rh (0.008 μg/l). The highest metal concentrations obtained in the sediment samples were Ni (85.1 mg/kg dry weight (d.wt)), Pb (25.4 mg/kg d.wt), Cu (75.5 mg/kg d.wt), Cd (64.9 mg/kg d.wt), Pt (0.38 ng/g d.wt), Pd (0.74 ng/g d.wt) and Rh (0.23 ng/g d.wt). The results obtained for the bioavailability studies of all the metals investigated in the sediment have revealed no definite patterns for the fractionation results of the metal concentrations. In the case of the crab samples collected in the Elands River, the Pb, Cd, Pt, Pd and Rh concentrations indicate that the mining activities may have had an influence in the uptake of these metals in the crab samples analysed. In the case of the Hex River, the Ni, Cu, Pb, Cd, Pd and Rh concentrations in the crab samples may be attributed to mining activities. The bioaccumulation results indicated that the Ni and Cu concentrations show partly bioaccumulation in the tissues of the crab samples evaluated. For the Pd, Cd, Pt, Pd and Rh concentrations evaluated, definite signs of bioaccumulation were found.

With the gradual depletion of high-grade copper ore deposits, secondary wastes are gaining importance as a source for metal recovery. However, the alkalinity and low copper concentration in some of these resources underscore the need for selective leaching agents. In this work, indigenous alkaliphiles from a fly ash landfill site with inherent pH tolerance, metal tolerance and copper leaching capability were isolated and investigated. Four isolates, namely Agromyces aurantiacus TRTYP3, Alkalibacterium pelagium TRTYP5, Alkalibacterium sp. TRTYP6 and Bacillus foraminis TRTYP17, each selectively leached about 50 % copper from 1 % (w/v) of fly ash. Mixed culture of these bacteria resulted in higher leaching of copper. The optimal combination was TRTYP3, TRTYP5, TRTYP6 and TRTYP17 in the ratio 1:1:3:1, which leached 88, 81, 78, 76, 70 and 55 % Cu from 1, 2.5, 5, 10, 15 and 20 % (w/v) of fly ash. While Cu and Pb were bioleached into solution, Fe and Zn were precipitated.

Iodinated contrast media (ICM), which are used for radiological visualization of human tissue and cardiovascular system, are poorly biodegradable; hence, new methods of their removal are sought. In this study, the effectiveness of selected X-ray ICM removal by means of UV and UV/TiO₂pretreatment processes from synthetic hospital wastewater was demonstrated. The following compounds were investigated: iodipamide, iohexol, and diatrizoate. The experiments were as follows: (i) estimated susceptibility of the ICM to decay by UV radiation in different aquatic matrices, (ii) determined an optimal retention time of hospital wastewater in the UV reactor, (iii) determined optimum TiO₂concentration to improve the effectiveness of the UV pretreatment, and (iv) investigated removal of ICM by combination of the photochemical and biological treatment methods. The quantum yields of selected ICM decay in deionized water (pH = 7.0) were established as 0.006, 0.004, and 0.029 for iohexol, diatrizoate, and iodipamide, respectively. Furthermore, the experiments revealed that diatrizoate and iohexol removal in the UV/TiO₂process is more efficient than in UV process alone. For diatrizoate, the removal efficiency equaled to 40 and 30 %, respectively, and for iohexol, the efficiency was 38 and 27 %, respectively. No significant increase in iodipamide removal in UV and UV/TiO₂processes was observed (29 and 28 %, respectively). However, highest removal efficiency was demonstrated in synthetic hospital wastewater with the combined photochemical and biological treatment method. The removal of diatrizoate and iohexol increased to at least 90 %, and for iodipamide, to at least 50 %.