Trade-offs between elimination and detoxification in rainbow trout and common bivalve molluscs exposed to metal stressors

The purpose of this paper was to examine trade-offs between elimination and detoxification in rainbow trout and three common bivalve molluscs (clam, oyster, and scallop) exposed to cadmium (Cd), copper (Cu), and zinc (Zn) based on recent reported experimental data. We incorporated metal influx threshold with subcellular partitioning to estimate rate constants of detoxification (k_d) and elimination (k₂). We found that the relationships between k₂ and k_d were negative for rainbow trout and positive for bivalve molluscs. However, the relationships between k_d and % metal in metabolically detoxified pool were found positive for rainbow trout and negative for bivalve molluscs. Our results also indicated that rainbow trout had higher accumulation (∼60-90%) in metabolically active pool when exposed to essential metals of Cu and Zn and had only 10-50% accumulation in response to non-essential metal of Cd. Based on a cluster analysis, this study indicated that similarity of physiological regulations among study species was found between Cd and Zn. Our study suggested that detoxification can be predicted by an elimination-detoxification scheme with the known elimination rate constant. We concluded that quantification of trade-offs between subcellular partitioning and detoxification provides valuable insights into the ecotoxicology of aquatic organisms and enhances our understanding of the subcellular biology of trace metals.     

Partitioning of metals in a degraded acid sulfate soil landscape: influence of tidal re-inundation

The oxidation and acidification of sulfidic soil materials results in the re-partitioning of metals, generally to more mobile forms. In this study, we examine the partitioning of Fe, Cr, Cu, Mn, Ni and Zn in the acidified surface soil (0-0.1 m) and the unoxidised sub-soil materials (1.3-1.5 m) of an acid sulfate soil landscape. Metal partitioning at this acidic site was then compared to an adjacent site that was previously acidified, but has since been remediated by tidal re-inundation. Differences in metal partitioning were determined using an optimised six-step sequential extraction procedure which targets the “labile”, “acid-soluble”, “organic”, “crystalline oxide”, “pyritic” and “residual” fractions. The surficial soil materials of the acidic site had experienced considerable losses of Cr, Cu, Mn and Ni compared to the underlying parent material due to oxidation and acidification, yet only minor losses of Fe and Zn. In general, the metals most depleted from the acidified surface soil materials exhibited the greatest sequestration in the surface soil materials of the tidally remediated site. An exception to this was iron, which accumulated to highly elevated concentrations in the surficial soil materials of the tidally remediated site. The “acid-soluble”, “organic” and “pyritic” fractions displayed the greatest increase in metals following tidal remediation. This study demonstrates that prolonged tidal re-inundation of severely acidified acid sulfate soil landscapes leads to the immobilisation of trace metals through the surficial accumulation of iron oxides, organic material and pyrite.     

Responses of a soil bacterium, Pseudomonas chlororaphis O6 to commercial metal oxide nanoparticles compared with responses to metal ions

The toxicity of commercially-available CuO and ZnO nanoparticles (NPs) to pathogenic bacteria was compared for a beneficial rhizosphere isolate, Pseudomonas chlororaphis O6. The NPs aggregated, released ions to different extents under the conditions used for bacterial exposure, and associated with bacterial cell surface. Bacterial surface charge was neutralized by NPs, dependent on pH. The CuO NPs were more toxic than the ZnO NPs. The negative surface charge on colloids of extracellular polymeric substances (EPS) was reduced by Cu ions but not by CuO NPs; the EPS protected cells from CuO NPs-toxicity. CuO NPs-toxicity was eliminated by a Cu ion chelator, suggesting that ion release was involved. Neither NPs released alkaline phosphatase from the cells’ periplasm, indicating minimal outer membrane damage. Accumulation of intracellular reactive oxygen species was correlated with CuO NPs lethality. Environmental deposition of NPs could create niches for ion release, with impacts on susceptible soil microbes.     

Mobility of Cd and Cu in formulated sediments coated with iron hydroxides and/or humic acids: a DGT and DGT-PROFS modeling approach

The diffusive gradients technique in thin films (DGT) was used to investigate the kinetic resupply of Cd and Cu to pore water from the solid phase. For the sake of simplification, experiments were performed using formulated sediments that differed in the presence or absence of humic acids (HA) and/or of iron hydroxides (i.e., goethite and ferrihydrite). The effects of the time after the contamination of the solid phase (aging effect) on formulated sediments that were coated with goethite and HA and spiked with Cd were also evaluated. Kinetic DGT results were interpreted using the newly developed, multi-compartmental model DGT-PROFS.Due to Cu humate formation, the addition of HA slightly increased the Cu concentration in the pore water independent of the effect of the iron hydroxide coating on the formulated sediments and slightly decreased that of Cd. The impact of 8-190 d of aging resulted in a significant decrease in the Cd concentration of the pore water over an increasing incubation time.Modeling our results with DGT-PROFS led to the following conclusions concerning the impact of HA and iron hydroxides on Cd and Cu availability. First, in the presence of HA and absence of iron hydroxides, Cd is associated mainly with weak sites, while Cu is bound to strong sites. Similarly, in the presence of both iron hydroxides and HA, Cu appeared to be more heavily associated with the strong sites than did Cd. When the incubation time increased from 8 to 190 d, a proportion of Cd initially adsorbed onto weak sites transferred to the strong sites, suggesting that the adsorption of Cd on sediments is controlled partially by slow kinetic processes.     

Biofilm responses to marine fish farm wastes

The changes in the biofilm community due to organic matter enrichment, eutrophication and metal contamination derived from fish farming were studied. The biofilm biomass, polysaccharide content, trophic niche and element accumulation were quantified along an environmental gradient of fish farm wastes in two seasons. Biofilm structure and trophic diversity was influenced by seasonality as well as by the fish farm waste load. Fish farming enhanced the accumulation of organic carbon, nutrients, selenium and metals by the biofilm community. The accumulation pattern of these elements was similar regardless of the structure and trophic niche of the community. This suggests that the biofilm communities can be considered a reliable tool for assessing dissolved aquaculture wastes. Due to the ubiquity of biofilms and its wide range of consumers, its role as a sink of dissolved wastes may have important implications for the transfer of aquaculture wastes to higher trophic levels in coastal systems.     

Comparison of Four <Emphasis Type="Italic">Sesbania</Emphasis> Species to Remediate Pb/Zn and Cu Mine Tailings

A 6-month greenhouse pot trial was performed, aimed at screening appropriate Sesbania species for remediation of Pb/Zn and Cu mine tailings. Performances of young seedlings of four Sesbania species (S. cannabina, S. grandiflora, S. rostrata, and S. sesban) were compared with and without inoculation of rhizobia. Seedlings were planted in two types of tailings amended with garden soil or garden soil mixed with river sediment. The results indicated that inoculated plants generally produced a higher biomass than samples without inoculation. Pb/Zn mine tailings containing rather high concentrations of total and water-soluble Cu, Pb, and Zn were toxic to plant growth compared with Cu mine tailings, according to the growth performance of the four species. Sesbania sesban and S. rostrata showed superior growth performance, compared to the other two species. Thus, they can serve as pioneer species to modify the barren environment, by providing organic matter and essential nutrients such as nitrogen, upon decomposition, in a relatively short period of time. This is especially true for S. rostrata, which is an annual plant that forms both stem and root nodules. However, a longer-term field trial should be conducted to investigate if superior species can beneficially modify the habitat for the growth of subsequent plant communities.     

Persistent Impacts of Trace Metals from Mining on Floodplain Grass Communities Along Soda Butte Creek, Yellowstone National Park

Phleum pratense and Poa pratensis were significantly lower (P ≤ 0.001) on plots with more than 250 ppm copper. Above-ground biomass of Phleum pratense was also significantly lower on plots with copper levels above 250 ppm. Decreased mean grass density was found on plots with pH < 6.4, but the only statistically significant difference was for Juncus balticus, which had increased density on plots with pH < 6.4. In contrast to the clear impacts of trace metals and pH on vegetation, other site characteristics did not alter measured vegetation characteristics.     

Insights into metals in individual fine particles from municipal solid waste using synchrotron radiation-based micro-analytical techniques

Excessive inter-contamination with heavy metals hampers the application of biological treatment products derived from mixed or mechanically-sorted municipal solid waste (MSW). In this study, we investigated fine particles of < 2 mm, which are small fractions in MSW but constitute a significant component of the total heavy metal content, using bulk detection techniques. A total of 17 individual fine particles were evaluated using synchrotron radiation-based micro-X-ray fluorescence and micro-X-ray diffraction. We also discussed the association, speciation and source apportionment of heavy metals. Metals were found to exist in a diffuse distribution with heterogeneous intensities and intense hot-spots of < 10 μm within the fine particles. Zn-Cu, Pb-Fe and Fe-Mn-Cr had significant correlations in terms of spatial distribution. The overlapped enrichment, spatial association, and the mineral phases of metals revealed the potential sources of fine particles from size-reduced waste fractions (such as scraps of organic wastes or ceramics) or from the importation of other particles. The diverse sources of heavy metal pollutants within the fine particles suggested that separate collection and treatment of the biodegradable waste fraction (such as food waste) is a preferable means of facilitating the beneficial utilization of the stabilized products.     

纳污湿地上覆水中重金属的监测及评价

以武河湿地为研究区域采集上覆水水样,采用ICP-AES法测定湿地水体中重金属的含量,参照有关标准用水质标准级别法对水中重金属污染情况进行了评价。结果表明:武河湿地中重金属Hg污染十分严重,各采样点均有分布且水质属劣Ⅴ类。重金属元素Cd污染并不严重,总体水质较好。重金属元素As、Cr、Cu、Pb在武河湿地中污染较轻近乎无污染,水质为Ⅰ类。由于重金属Hg的污染十分严重所以研究区内综合质量等级在4以上,水质为Ⅴ类和劣Ⅴ类,污染严重。