Analysis and risk assessment of pharmaceutical residues in fish from three water bodies in Ghana.

Illegal mining has overshadowed pharmaceutical pollution even though exposure to pharmaceutical waste is high. Consumption of fish potentially polluted with pharmaceuticals from the rivers continues with little concern or potential threat it poses. In the present study, the residues of one antibiotic (Chloramphenicol), five hormones (progesterone, 17-beta Estradiol, Estrone, 17a-Ethynylestradiol, and one), three environmental contaminants (4-para-nonylphenol, 4-tert-octylphenol, and Bisphenol A), one barbiturate (Primidone) and one analgesic (Diclofenac sodium salt), were investigated from fish samples from the rivers Pra, Narkwa, and the Volta. The results show a high concentration of drugs in River Pra in comparison to those in Rivers Narkwa and Volta. The hazard quotients (HQs) for the environmental contaminants were all above 1, except Bisphenol A. Furthermore, the HQs from this study suggest that consumers of fish from any of the three rivers stand a hazard risk of Chloramphenicol (19), 17a-Ethynylestradiol (4), Estrone (1.366), Diclofenac sodium salt (3.29), Progesterone (4.598), 4-tert-octylphenol (87.2), and 4-para-nonylphenol (7.252), but negligible risk against E2 (0.687), Primidone (0.014), Testosterone (0.16), and Bisphenol A (0.642). Of the fish species studied, the highest concentration of all pharmaceuticals put together is found in Clarias gariepinus, Labeo senegalensis, and Chrysichthys nigrodigitatus in that order.

New insight into the adsorption mechanism of PCP by humic substances with different degrees of humification in the presence of Cr(VI).

Humic substances (HSs) have great retention effects on pentachlorophenol (PCP) migration in subsurface environment, but the adsorption mechanism of PCP by HSs with various aromatic/aliphatic moieties and acidic functional groups in the presence of Cr(VI) is still unclear. In this study, the adsorption mechanism of PCP by undissolved humic acid (HA) and humin (HM) extracted from peat, black soil, lignite and coal was investigated under the presence of Cr(VI). According to the results, HA samples had much lower adsorption capacity for hydrophobic PCP than HM samples due to their higher contents of hydrophilic polar oxygen-containing functional groups. In respect to PCP adsorption mechanism, the molecular unsaturation of HSs associated with humification degree was found to be the determinant instead of polarity. Notably, after reacting with Cr(VI), significant decreasing of PCP adsorption quantities occurred on HSs extracted from lignite and coal with higher degrees of unsaturation (H/C < 0.64), while HSs extracted from peat and black soil with lower degrees of unsaturation (H/C > 0.83) kept almost unchanged, which can be attributed to the much higher reactivity of aromatic domains of HSs for Cr(VI) reduction compared with aliphatic moieties. This indicated that the adsorption mechanism of PCP by HSs with higher and lower degrees of unsaturation might be respectively driven by π-π interaction and hydrophobic interaction. This study highlighted the diverse adsorption mechanisms of PCP on HSs with different degrees of humification, and emphasized the coexisting Cr(VI) only have significant effect on PCP adsorption by HSs with higher humification degrees instead of the lower ones.

Natural attenuation mechanism of hexavalent chromium in a wetland: Zoning characteristics of abiotic and biotic effects.

Natural wetland has great retention effect on Cr(VI) migration due to its abiotic and biotic reduction abilities, however, the zoning characteristics of dominating reduction mechanism along Cr(VI) pollution plume in wetland is still unclear. In this study, a Cr(VI) contaminated natural wetland was explored to investigate the distributions of Cr and Fe in groundwater and sediment, and their relationship with microorganisms according to metagenomics, aiming to reveal the natural attenuation mechanism of Cr(VI) from the perspective of zoning characteristics of abiotic and biotic effects. The wetland was divided into contaminated zone, transition zone and uncontaminated zone according to the contamination states of groundwater and sediment. At the upstream of contaminated zone, Cr(VI) concentration in groundwater was as high as 26.7 mg L-1, which has significant inhibition effect on microbial growth, and thus chemical reduction of Cr(VI) by natural organic matters (NOMs) dominated in this area, leading to the increasing of H/C and O/C ratios of NOMs because of the oxidation of aromatic moieties. At the downstream of contaminated zone, Cr(VI) concentration in groundwater decreased to less than 4.46 mg L-1 resulting from dilution and attenuation, but the microbial community was altered substantially, chromate resistant bacteria with ChrA, ChrR, NemA and AzoR genes were enriched, such as Sphingomonas, Mesorhizobium and Comamonadaceae, and thus the direct microbial reduction of Cr(VI) dominated in this area. While at the transition zone, which is located at the front edge of the pollution plume, Cr(VI) could only reached in this area intermittently, and the microbial community remained similar to that of the uncontaminated zone, dominated by Chloroflexi and Acidobateria phylum with dissimilatory ferric iron reduction capacity, and thus Cr(VI) was indirectly reduced by Fe2+ intermediately in this area.

Mechanism and multi-step kinetic modelling of Cr(VI) adsorption, reduction and complexation by humic acid, humin and kerogen from different sources.

Humin (HM) and kerogen (KG) are widespread in soils and sediments, which have strong retention effects on the migration and transformation of Cr(VI) in subsurface environment. Previous studies mainly focused on the interaction between Cr(VI) and soluble organic matter, such as humic acid (HA); however, the adsorption and reduction mechanism for Cr(VI) by insoluble HM and KG are still unclear, the processes of which might be quite different from HA due to their different sources and humification degrees. Consequently, in this study, HA, HM and KG extracted from different sources were used to explore the adsorption, reduction and complexation mechanisms of Cr(VI) in soils and sediments, based on which a multi-step kinetic model of Cr(VI) was carried out. According to the results, the retention of Cr(VI) by humus was found to obey a coupling mechanism of "adsorption-reduction-complexation", where Cr(VI) adsorption was by complexation with carboxylic groups by ligand exchange. The phenolic and hydroxylic groups were determined to be the main electron donor for Cr(VI) reduction. Notably, the Cr(III) produced was found to be adsorbed on the surface of humus by complexation on phenolic and hydroxylic groups, and the excesses were released into the liquid phase after the saturation of complexation sites. Based on the revealed mechanism, a multi-step kinetic model for simultaneously describing Cr(VI) adsorption and reduction and behaviour of Cr(III) was proposed producing a better fitting performance (R2 ≥ 0.984) than the first-order and second-order kinetic models (R2 ≤ 0.84 and 0.87, respectively) and hence could provide more factual understanding of Cr(VI) transformation in soils and sediments enriched in various types of humus.

Mechanism and modeling of hexavalent chromium interaction with a typical black soil: the importance of the relationship between adsorption and reduction.

Black soils have a significant retention effect on the migration of Cr(vi) towards groundwater, and Cr(vi) adsorption and reduction are both involved in this process. However, the adsorption and reduction of Cr(vi) were always investigated separately in previous studies resulting in an unclear relationship between them. In this study, the adsorption and reduction kinetic processes of Cr(vi) by a typical black soil were separately investigated under different initial Cr(vi) concentrations (40-400 mg L-1) and pH conditions (3.5-7.0) by the means of desorption treatment, and the equilibrium relationship between aqueous and adsorbed Cr(vi) was innovatively established based on the kinetic data. It was found that under pH 5.7 the adsorbed Cr(vi) content on soil particles was linearly correlated with the remaining Cr(vi) concentration in solution with time (R 2 = 0.98), and the reduction rate of Cr(vi) in the reaction system was linearly correlated with the adsorbed Cr(vi) content on soil particles with time (R 2 = 0.99). With pH decreasing from 7.0 to 3.5, the partition of Cr(vi) between solid and aqueous phases turned out to be of a non-linear nature, which can be fitted better by the Freundlich model. The retention of Cr(vi) by black soil was determined to follow the "adsorption-reduction" mechanism, where the Cr(vi) was first rapidly adsorbed onto the soil particles by a reversible adsorption reaction, and then the adsorbed Cr(vi) was gradually reduced into Cr(iii). A two-step kinetic model was developed accordingly, and the experimental data were fitted much better by the two-step adsorption-reduction kinetic model (R 2 = 0.89 on average) compared with the traditional first-order and second-order kinetic models (R 2 = 0.66 and 0.76 on average respectively). This paper highlights the novel two step kinetic model developed based on the proposed "adsorption-reduction" mechanism of Cr(vi) retention by a typical black soil.

The influence of pH, co-existing ions, ionic strength, and temperature on the adsorption and reduction of hexavalent chromium by undissolved humic acid.

The retention of Cr(VI) in subsurface environment is highly dependent on humic acid (HA), however, the undissolved form is poorly investigated, the amount of which can be of two magnitude higher compared with the dissolved one in soils and sediments. In this study, the effects of time, initial concentration, pH, ionic strength, ion species and temperature on the adsorption and reduction respective processes by undissolved self-extracted peat soil HA from Northeast China (EHA) and from Sigma Aldrich (CHA) were investigated by batch experiments. Cr(VI) removal rates by EHA were higher than CHA and the maximum Cr(VI) removal amount for EHA and CHA were 0.77 (±0.01) and 0.61 (±0.02) mmol/g. Of these, 98% and 54% were reduced to Cr(III) by EHA and CHA respectively, which were related to the phenolic group content of HA. With time, the adsorbed Cr(VI) on HA increased to a maximum level (equilibrium) beyond which Cr(VI) reduction dominated the removal process. Cr(VI) adsorption and reduction by undissolved HA increased as pH decreased. Co-existing ion species had varying effect on Cr(VI) adsorption and indirectly on reduction especially divalent cations which was suggestive of cation bridging between Cr anions and ionized carboxyl group of HA. The positive effect of ionic strength (Ca2+) on Cr(VI) adsorption through complexation corroborated the cation bridge effect of divalent cations. Temperature increased both Cr(VI) adsorption (complexation) and reduction with enhancing reduction rate constants and partitioning. ΔHo, ΔSo, and ΔG° parameters showed that Cr(VI) adsorption and reduction processes were endothermic, irreversible and spontaneous.