Concentrations Of Metal Contaminants Research Articles

An updated ecotoxicological evaluation and health risk assessment of metal contaminants in Perna viridis mussel harvested on March to August 2018 from Pasir Gudang Coastal Area, Malaysia

Perna viridis (P. viridis) is a significant protein source globally but is often contaminated by metals due to its filter-feeding behavior. Given that Kampung Pasir Puteh, Pasir Gudang (Johor) is Malaysia's primary P. viridis harvesting site and the last health risk assessment (2015) was incomplete, the metal contamination status remains uncertain. Graphite furnace-atomic absorption spectroscopy was employed to analyze metal contaminant concentrations in P. viridis samples collected from March to August 2018, as per Malaysian legal requirements. The R2 values varied between 0.9976 and 0.9980 for P. viridis mussels and between 0.9976 and 0.9999 for seawater. The recovery for P. viridis mussels and seawater ranged from 93.95% to 106.80% and 92.73–108.84%, respectively. Precision and accuracy for both intra and inter-day measurements ranged from 0.15% to 5.49% for P. viridis and 0.05–5.58% for seawater. The concentrations of metal contaminants in P. viridis varied significantly among the different months of sampling (p < 0.05). All P. viridis samples had higher concentration of arsenic (3.16–75.80 μg g−1) than that prescribed by the Malaysian law. Higher cadmium concentration was observed during July (2.12 μg g−1) and August (2.05 μg g−1) alone. With target hazard quotients and hazard indices > 1.0, the likelihood of negative health impacts from consuming these mussels cannot be ignored. TCR values for As and Cd exceeded USEPA standards, indicating a potential lifetime carcinogenic risk from continuous P. viridis consumption. Pb (21.20–49.28 µg L−1) in all surface seawater samples was invariably higher than the allowable limit for Class 2 water areas. Metal contaminant concentrations varied significantly between P. viridis and surface seawater (p < 0.05), implying inconsistent bioaccumulation due to pollution differences. Given the significance of P. viridis mussels, concerted scientific efforts are essential to devise effective metal contaminant removal methods.

An Assessment of aluminum contamination in neonatal parenteral nutrition solutions based on measured versus labeled content

Aluminum can potentially cause toxicity in pediatrics and neonates receiving parenteral nutrition. Some PN solutions and ingredients in Saudi Arabia do not comply with US FDA regulations regarding aluminum exposure. This study aims to determine the aluminum concentration in samples of PN solutions and ingredients used to feed infants in Saudi Arabia. The aluminum in the samples was determined using inductively coupled plasma mass spectrometry. The concentration of metal contaminants in each sample was determined in triplicate. The aluminum content of 38 samples was investigated, 15 of which originated from components included in the prepared PN solutions. Among the 15 samples, the least measurable aluminum content was detected in potassium chloride solutions (0.81 mcg/L). In contrast, the greatest amount of aluminum was detected in potassium phosphate and calcium gluconate (141,64 mcg/L and 462.7 mcg/L), respectively. The results showed that the final PN solution (PNS) product contained more aluminum levels than the content ingredients; in addition, the study found a statistically significant relationship among 18 pediatric patients at KFMC who had intestinal failure and needed long-term parenteral nutrition. Specifically, their high aluminum levels, exceeding the normal range of 0.6 ng/ml, indicate that the current use of PN solutions will likely cause toxicity due to aluminum contamination in additives. Hence, reducing aluminum in PN solutions is imperative to ensure patient safety.

Nanocrystal Preparation of Poorly Water-Soluble Drugs with Low Metal Contamination Using Optimized Bead-Milling Technology.

Nanocrystal preparation using bead milling is an important technology to enhance the solubility of poorly water-soluble drugs. However, there are safety concerns regarding the metal contaminants generated during bead milling. We have previously reported optimized bead-milling parameters that could minimize metal contamination and demonstrated comparable performance to NanoCrystal®, a world-leading contamination-free technology. This study aimed to investigate the applicability of optimized milling parameters for preparing nanocrystals of several poorly water-soluble drugs exhibiting various physicochemical properties. Using our optimized bead-milling parameters, we found that all the tested drugs could be ground into nanosized particles within 360 min. Notably, fenofibrate, which has a low melting point, could be ground into nanosized particles owing to the low level of heat generated during bead milling. Additionally, the concentration of metal contaminants in all the drugs prepared using the optimized milling parameters were approximately ten to twentyfold lower than those prepared without the optimized parameters and were comparable to those prepared using polycarbonate beads, known to minimize metal contamination during bead milling. Our results provide insights into the development of drug nanocrystals with low metal contamination using bead milling.

Metal contaminants and chloramphenicol in Litopenaeus vannamei and Penaeus silasi at various supply chain stages in Johor Bahru, Malaysia and their health risk assessment

ObjectivesThis present research evaluated the concentrations of metal contaminants (As, Pb, Cd and total Hg) and chloramphenicol as prescribed by the Malaysian Food Act (1983) and Regulations (2021) in Penaeus silasi and Litopenaeus vannamei shrimps sampled from the different supply chain stages (landing sites, major markets and grocers) in Johor Bahru, Johor, Malaysia at six sampling intervals. MethodsGraphite furnace atomic absorption spectrometer and flow injection mercury/hyride system were used to determine the concentration of As, Pb and Cd as well as total Hg, respectively. Enzyme-linked immunosorbent assay was used to determine the concentration of chloramphenicol. ResultsThe median As and Cd concentrations during the six sampling intervals ranged between below detection limit-167.5 mg/kg and 0.46 mg/kg, respectively. The total Hg concentrations ranged between 0.02 and 1.13 mg/kg. Although Pb and chloramphenicol were not detected, As and total Hg concentrations varied significantly across sampling intervals (P < 0.05), exceeded the maximum permitted proportions prescribed by the Malaysian law. Identified as P. silasi, shrimps from landing sites Mersing and Pontian had significantly higher As and total Hg concentrations than those of L. vannamei from major markets and their surrounding grocers (P < 0.05). Alarmingly, Hazard Index for P. silasi from landing sites Mersing and Pontian as well as L. vannamei from major markets and grocers exceeded 1.00. ConclusionHence, formulating suitable intervention programs and devising efficient removal technologies are paramount for benefiting the public at large.

Quantifying and characterising metal concentrations in Derwent Estuary sediments using portable X-ray fluorescence spectrometry

The Derwent Estuary is highly enriched in potentially toxic elements, such as Zn, Pb, Cu, As, Hg and Cd, owing to inputs from historical industrial activity adjacent to the river, predominantly prior to strict environmental protections introduced in the 1970s. Contaminants are now buried at shallow depths within the sediment profile, in one or two highly concentrated layers decreasing in concentration away from an electrolytic zinc refinery, regarded as the main source of the contaminants. Enriched metals (Zn, Pb, Cu, Cd and As) in the estuary were estimated from data collected from 37 sediment cores using a portable X-ray fluorescence spectrometer that was validated against inductively coupled plasma mass spectrometer analyses. The thickness of the metal and metalloid enriched layers ranges from 32.5 to 107.5 cm, with an average thickness of 63 cm. Sedimentation rates based on this layer and the time since the start of zinc processing are approximately 0.46 cm/year. Sedimentation rates based on the thickness since maximum metal and metalloid concentrations are between 0.17 and 1.64 cm/year. Based on these sedimentation rates, the average time it will take for surface sediments to return to background metal and metalloid concentrations, if left undisturbed, is approximately 123 years. KEY POINTS Metal contaminant concentrations in Derwent Estuary sediments have two clear peaks in concentrations at depth, where estuary sediments have been enriched at varying rates over the last 97 years. The contaminated layer varies in thickness throughout the estuary, but has an average thickness of 63 cm, a maximum thickness of 107.5 cm and a minimum thickness of 32.5 cm, from surface sediments to the bottom of contamination. All surface sediments were enriched in metals or metalloids, but the overall trend in metal concentrations is decreasing from a major enrichment peak to moderate concentrations at the sediment–water interface. The time required for surface sediments to return to acceptable concentrations as defined by the ISQG is estimated to be on average 123 ± 88 years for the whole estuary with different parts of the estuary returning to background at different times.

WaterQuality Guidelines for Metal Contaminants in Stormwater Runoff: Insights and Considerations.

WaterQuality Guidelines for Metal Contaminants in Stormwater Runoff: Insights and Considerations.

Uranium and metal concentrations in community water systems across the United States, 2006-2011

BACKGROUND AND AIM: The US Environmental Protection Agency (EPA) sets maximum contaminant levels (MCLs) for 9 metals/metalloids in public drinking water systems. Beyond arsenic, no nationwide exposure estimates for public drinking water currently exist for these contaminants. Our objective was to estimate exposure to metals in community water systems (CWSs) across the US, to determine if sociodemographic or regional inequalities in these exposures exist, and to identify patterns of exposure for these metals as a mixture. METHODS: We evaluated routine compliance monitoring records for antimony, barium, beryllium, cadmium, chromium, mercury, selenium, thallium, and uranium collected from 2006-2011 (2000-2011 for uranium) by the US EPA in support of the Third Six Year Review for 37,915 CWSs. We focused our analysis on barium, chromium, selenium, and uranium (as arsenic has been reported previously and other metals were mostly undetected), comparing the mean contaminant concentration and the percent of CWSs with MCL excedances across subgroups (US region, sociodemographic county-cluster, size of population served, source water type, and correctional facilities). We evaluated patterns in metal exposure profiles via hierarchical cluster analysis, which also included published CWS arsenic estimates. RESULTS:The percentage of CWSs exceeding the MCL was highest for uranium (3.1% MCL of 30 µg/L, nationwide mean 4.37 µg/L), but lower than previously reported arsenic (2.6%). 75th, 95th percentiles for uranium, chromium, barium, and selenium concentrations were highest for CWSs serving {Semi-Urban, Hispanic} communities, small CWSs, CWSs reliant on groundwater, and those located in the Southwest, similar to previous CWS arsenic findings. Hierarchical cluster analysis revealed four clusters, including an arsenic-uranium-selenium cluster. CONCLUSIONS:{Semi-Urban, Hispanic} communities experience higher average concentrations of metal contaminants, including uranium and arsenic, in public drinking water. Uranium is an under-recognized contaminant in CWSs. Cluster analyses revealed that arsenic and uranium may co-occur in groundwater sources serving CWSs. KEYWORDS: exposure, environmental justice, environmental disparities, water quality

Sublethal effects of contaminants on marine habitat-forming species: a review and meta-analysis.

ABSTRACTContaminants may affect ecosystem functioning by reducing the fitness of organisms and these impacts may cascade through ecosystems, particularly if the sensitive organisms are also habitat‐forming species. Understanding how sub‐lethal effects of toxicants can affect the quality and functions of biogenic habitats is critical if we are to establish effective guidelines for protecting ecosystems. We carried out a global systematic review and meta‐analysis critically evaluating contaminant effects on properties of habitat‐formers linked to ecosystem functioning. We reviewed a total of 95 publications. However, 40% of publications initially captured by the literature search were identified as having flaws in experimental design and ~11% did not present results in an appropriate way and thus were excluded from the quantitative meta‐analysis. We quantitatively reviewed 410 studies from 46 publications, of which 313 (~76%) were on plants and seaweeds, that is macro‐algae, saltmarsh plants and seagrasses, 58 (~14%) studied corals and 39 (~10%) looked at toxicant impacts on bivalves, with 70% of those on mussels and the remaining studies on oysters. Response variables analysed were photosynthetic efficiency, amount of chlorophyll a (as a proxy for primary production) and growth of plants, seaweeds and corals as well as leaf area of plants. We also analysed filtration, growth and respiration rates of bivalves. Our meta‐analysis found that chemical contaminants have a significant negative impact on most of the analysed functional variables, with the exception of the amount of chlorophyll a. Metals were the most widely harmful type of contaminant, significantly decreasing photosynthetic efficiency of kelps, leaf area of saltmarsh plants, growth of fucoids, corals and saltmarsh plants and the filtration rates of bivalves. Organic contaminants decreased the photosynthetic efficiency of seagrass, but had no significant effects on bivalve filtration. We did not find significant effects of polycyclic aromatic hydrocarbons on any of the analysed functional variables or habitat‐forming taxa, but this could be due to the low number of studies available. A meta‐regression revealed that relationships between concentrations of metal contaminants and the magnitude of functional responses varied with the type of metal and habitat‐former. Increasing concentrations of contaminants significantly increased the negative effects on the photosynthetic efficiency of habitat‐formers. There was, however, no apparent relationship between ecologically relevant concentrations of metals and effect sizes of photosynthetic efficiency of corals and seaweeds. A qualitative analysis of all relevant studies found slightly different patterns when compared to our quantitative analysis, emphasising the need for studies to meet critical inclusion criteria for meta‐analyses. Our study highlights links between effects of contaminants at lower levels of organisation (i.e. at the biochemical and/or physiological level of individuals) and ecological, large‐scale impacts, through effects on habitat‐forming species. Contaminants can clearly reduce the functioning of many habitat‐forming marine species. We therefore recommend the adoption of routine measures of functional endpoints in monitoring and conservation programs to complement structural measures.

Effect of CuSO4 on the Hydromechanical Behavior of Compacted Tailings

Laboratory tests, including compressibility, permeability, and microstructure tests, were conducted on tailings samples using custom-designed test apparatus to investigate the effect of metal contamination (Cu2+) on the hydromechanical behavior of compacted tailings. Infiltrating samples with various dry densities with distilled water or CuSO4 solution at various concentrations showed that the void ratio of compacted tailings decreased with increased dry density. An increase in the metal contaminant concentrations from 0 to 0.1 mol/L increased the compression coefficient of the tailings from 0.14 to 0.84 MPa−1 under a vertical load of 0.01 to 2.0 MPa, while the yield stress of the tailings decreased from 204.3 to 98.7 kPa, respectively. The linear relationship between permeability coefficient (k) and void ratio (e) is described by k = − 6.48 + 17.17e. Microstructure test results showed that the diffusion double layer thinned, and the surface potential decreased, indicating that the contaminant of Cu2+ enhanced the compressibility and permeability of the tailings. The microstructure test results also showed that the amount of fine-grained soil in the copper tailings was significantly less after the hydromechanical test. Therefore, the permeability and compressibility of copper tailings increased. The experimental results are in good agreement with the estimated results.

Water metal contaminants in a potentially mineral-deficient population of Haiti

ABSTRACTThis study aimed to characterize metal contaminant concentrations and assess temporal and spatial variability in the main drinking water sources of Cap-Haïtien, Haiti. Water sources from five communities were sampled in two seasons, June (2014) and October (2014), and analysed for a suite of metals. A geographic information system was used to examine the spatial distribution of sampling points. Metal concentrations were below the US Environmental Protection Agency (USEPA) primary drinking water standards. Mean manganese concentrations were comparatively higher in wells (254.5 µg/L), exceeding the USEPA secondary drinking water standard (50 µg/L). Higher mean Mg/Ca and Ba/Ca ratios (range 2.3–3.4) may indicate different interactions between seawater and groundwater throughout the year. Although metal concentrations were within the limits of the USEPA drinking water standards, emerging contaminants, such as manganese, showed concentrations in excess of recommended limits. These metals may interact with background nutritional status with potential implications for growth and development.

Bioaccumulation of mercury and other metal contaminants in invasive lionfish (Pterois volitans/miles) from Curaçao

A wide range of ecological and environmental factors influence metal bioaccumulation in fish. Studies of mercury and other metal contaminants in invasive Indo-Pacific lionfish are limited, yet consumption of the invasive predator is increasingly utilized as a management strategy. In this study, we examined the effects of body size, body condition, sex, trophic level, carbon source, diet, depth and capture location on mercury concentrations in lionfish collected from Curaçao. In addition, we examined whether or not a local petroleum refinery is the source of metal contamination in lionfish. Mercury concentrations ranged from 0.008 to 0.106 mg/kg and we found no effect of the petroleum refinery on metal bioaccumulation in lionfish. Low concentrations of metal contaminants indicate lionfish from Curaçao are safe for human consumption.

Metal accumulation by sunflower (Helianthus annuus L.) and the efficacy of its biomass in enzymatic saccharification

Accumulation of metal contaminants in soil as a result of various industrial and anthropogenic activities has reduced soil fertility significantly. Phytoextraction of metal contaminants can improve soil fertility and provide inexpensive feedstock for biorefineries. We investigated the hyperaccumulation capacity of sunflower (Helianthus annuus) biomass by cultivating these plants in various concentrations of metal contaminants. Sunflowers were grown in soils contaminated with various levels of heavy metals (10–2,000 mg/kg dry soil). The degree of metal uptake by different parts of the biomass and the residual concentration in the soil were estimated through inductively coupled plasma mass spectrometry. An almost 2.5-fold hyperaccumulation of Zn2+ was observed in the leaf and flower biomass compared with the concentration in the soil. For the subsequent saccharification of biomass with hyperaccumulated contaminants, a fungal lignocellulosic consortium was used. The fungal consortium cocktail retained more than 95% filter paper activity with 100 mM Ni2+ ions even after 36 h. The highest saccharification yield (SY, 87.4%) was observed with Ni2+ as the contaminant (10 mg/kg dry wt), whereas Pb2+ (251.9 mg/kg dry wt) was the strongest inhibitor of biomass hydrolysis, resulting in only a 30% SY. Importantly, the enzyme cocktail produced by the fungal consortium resulted in almost the same SY (%) as that obtained from a combination of commercial cellulase and β-glucosidase. Significant sugar conversion (61.7%) from H. annuus biomass hydrolysate occurred, resulting in the production of 11.4 g/L of bioethanol. This is the first study to assess the suitability of phytoremediated sunflower biomass for bioethanol production.

H emibagrus sp. as a potential bioindicator of hazardous metal pollution in Selangor River.

The spatial distributions of Na, Mg, K, Ca, Cr, Fe, Ni, Cu, Zn, As, Se and Pb in Hemibagrus sp. from Selangor River and a reference site were determined with inductively coupled plasma-mass spectrometer, in comparison to the levels in their surrounding water body and sediments. The results demonstrated significant differences in elemental accumulation pattern in different fish tissues originated from both sites. The variations observed were mainly subjected to their metabolic activities, and also the influence of the surrounding medium. In general, the liver tends to accumulate higher concentration of metals followed by the gills, and muscle tissues. The data also indicate associations between the concentrations of metal contaminants measured in the fish and the levels observed at the sites. The concentrations of hazardous metals As, Se and Pb in all the studied tissues reflect the influence of anthropogenic inputs. This suggests the potential utility of widely available Hemibagrus sp. as a valuable bioindicator of metal pollution in environmental monitoring and assessment.

Pongamia pinnata inoculated with Bradyrhizobium liaoningense PZHK1 shows potential for phytoremediation of mine tailings.

Mine tailings contain high concentrations of metal contaminants and only little nutrients, making the tailings barren for decades after the mining has been terminated. Effective phytoremediation of mine tailings calls for deep-rooted, metal accumulating, and soil fertility increasing plants with tolerance against harsh environmental conditions. We assessed the potential of the biofuel leguminous tree Pongamia pinnata inoculated with plant growth promoting rhizobia to remediate iron-vanadium-titanium oxide (V-Ti magnetite) mine tailing soil by pot experiment and in situ remediation test. A metal tolerant rhizobia strain PZHK1 was isolated from the tailing soil and identified as Bradyrhizobium liaoningense by phylogenetic analysis. Inoculation with PZHK1 increased the growth of P. pinnata both in V-Ti magnetite mine tailings and in Ni-contaminated soil. Furthermore, inoculation increased the metal accumulation capacity and superoxide dismutase activity of P. pinnata. The concentrations of Ni accumulated by inoculated plants were higher than the hyperaccumulator threshold. Inoculated P. pinnata accumulated high concentration of Fe, far exceeding the upper limit (1000mgkg-1) of Fe in plant tissue. In summary, P. pinnata-B. liaoningense PZHK1 symbiosis showed potential to be applied as an effective phytoremediation technology for mine tailings and to produce biofuel feedstock on the marginal land.

A novel coupled biokinetic-equilibrium model to capture oyster metal bioaccumulation in a contaminated estuary (Sydney estuary, Australia)

Enriched concentrations of metal contaminants have been reported in surficial sediments and tissues of aquatic organisms in Sydney estuary, New South Wales, Australia. Dietary ingestion of contaminated, suspended sediments is potentially a major route of metal exposure to the filter-feeder Saccostrea glomerata. A dynamically coupled biokinetic-equilibrium bioaccumulation model was developed to explore sediment-oyster-metal uptake interactions. The biokinetic component simulated the sediment dynamics and oyster uptake and loss kinetics while the ion equilibrium model accounted for the metal speciation reactions. Results of a laboratory-based mesocosm experiment as well as data from the literature were used to parameterise the model. The model demonstrated a good fit of the experimental data and indicated that dissolved and particulate organic matter were important determinants of metal bioavailability to this species. The model served also as a unique tool to formulate testable hypotheses and help to better explain the bioaccumulation patterns observed from the experiment.

Chemical composition of farmed and micropropagated Kappaphycus alvarezii (Rhodophyta, Gigartinales), a commercially important seaweed in Malaysia

Micropropagation technologies play an important role in enhancing the nutritional composition of seaweeds. Kappaphycus alvarezii explants, obtained from two types of seedling production system viz. micropropagation and farm propagation, were analyzed. Results obtained from the post-farm cultivation seaweeds showed significantly higher total lipids in micropropagated compared to farm-propagated K. alvarezii. In the mineral and trace element analyses, micropropagated K. alvarezii yielded significantly higher calcium, magnesium, beryllium, cobalt, copper, lithium, manganese, and zinc compared to farm-propagated K. alvarezii. A lower concentration of metal contaminants was detected in micropropagated K. alvarezii compared to farm-propagated K. alvarezii. Both sources of K. alvarezii showed high SFA compared to MUFA and PUFA, where C16:0 and C18:0 were found to be in abundance. The study suggests micropropagated K. alvarezii is a better food source for consumption compared to farm-propagated K. alvarezii and justifies the rationale of using micropropagation technique for seedling production in the seaweed industry.

Combined use of DGT and transplanted shrimp (Litopenaeus vannamei) to assess the bioavailable metals of complex contamination: implications for implementing bioavailability-based water quality criteria

The diffusive gradients in thin films (DGT) were field deployed alongside the shrimp Litopenaeus vannamei at seven sites with different levels of contamination to assess the potentially bioavailable and toxic fraction of metal contaminants. After 7 days of exposure, several antioxidant biomarkers were quantified in hepatopancreas of exposed shrimps, and tissue levels as well as the total, dissolved, and DGT-labile concentrations of metal contaminants were determined in the pooled site samples. The results showed that the caged shrimps had high tissue contaminant concentrations and significantly inhibited antioxidant responses at the more contaminated sites. DGT-labile metal concentrations provided better spatial resolution of differences in metal contamination when compared with traditional bottle sampling and transplanted shrimp. The total, dissolved, and DGT-labile metal fractions were used to evaluate the potential bioavailability of metal contaminants, comparing with metal accumulation and further linking to antioxidant biomarker responses in tissues of exposed shrimps. Regression analysis showed the significant correlations between DGT-Cu concentrations and tissue-Cu and activities of some biomarker responses in the shrimp hepatopancreas. This indicated that DGT-labile Cu concentrations provided the better prediction of produced biological effects and of the bioavailability than the total or dissolved concentrations. The study supports the use of methods combining transplanted organisms and passive sampling for assessing the chemical and ecotoxicological status of aqueous environments and demonstrates the capability of the DGT technique as a powerful tool for measuring the bioavailability-based water quality in variable coastal environments.

Cluster Analysis of Metal Concentrations in River Kubanni Zaria, Nigeria

The cluster analysis was used to assess the degree of association of the metal concentrations in river Kubanni Zaria, Nigeria. The main sources of data for the analysis were the sediment from four distinct locations along the long profile Kubanni River which were analyzed using Instrumental Nitrogen Activities Analysis (INAA) techniques. The Nigerian Research Reactor-1(NIRR-1) which is Miniature Nitrogen Source Reactor (MNSR) was used to analyze the data. The result of the laboratory analysis was subjected to cluster analysis. The analysis shows a stable clustering system where the metal concentrations in the four different locations were grouped into two main groups with one outlier. The level of concentration of elements that were sampled in the dry months were cluster in group I and those collected in the raining months were in group II. This strongly support that there is temporal variation in the levels of concentration of metal contaminants between wet and dry seasons in river Kubanni and also confirms the fact that the elements that were collected in the wet season are from the same source and those in the dry season are also from common source.

Improvement of Minority Carrier Lifetime by HCN Treatments

We have developed a method of improving minority carrier lifetime by use of HCN treatments. Metal contaminants, Fe, Ni, and Cu, are introduced during slicing Si ingots to produce Si wafers, and also during alkaline etching processes for removal of a damaged layer and formation of mat-textured surfaces. The concentrations of metal contaminants are greatly decreased by cleaning with HCN solutions having pH of 12, while they are decreased only slightly by pH 9 HCN solutions. Two kinds of metal contaminants, i.e., contaminants present deeply in saw damaged regions and on the surface due to re-adsorption during alkaline etching, can be removed by pH 12 HCN solutions while only the latter can be by pH 9 HCN solutions. The minority carrier lifetime is increased by removal of a damaged layer by alkaline etching but decreased below that of as-sliced wafers after formation of mat-textured surfaces. The lifetime is increased by the HCN treatment and it is attributed to i) removal of metal contaminants and ii) passivation of interface states by the formation of Si-CN bonds from Si dangling bonds.

Coupled interactions between metals and bacterial biofilms in porous media: Implications for biofilm stability, fluid flow and metal transport

The ability to predict the impact of metal–microbe interactions on biofilm stability, hydrodynamics and contaminant transport is a key goal in hydrogeology, membrane bioreactors and geomicrobiology. Yet, we have not been able to find experimental studies reporting the coupling of these three elements in a systematic way. In this study sand column experiments were carried out to investigate the coupled effects of aqueous zinc (Zn2+) on biofilm stability and of biofilm on Zn2+ transport in saturated sand columns. A series of aqueous Zn concentrations ranging from 0 to 100ppm were pumped through biofilm-colonised columns and a set of related parameters (hydraulic conductivity, cell numbers, EPS, metal breakthrough curve and metal distribution) was measured. Our results show that biofilm formation prior to introduction of Zn resulted in a significant decrease of hydraulic conductivities. After 10days of metal exposure, Zn showed concentration-dependent toxicity on bacterial cells in the biofilm. However different Zn concentrations produced distinct non-linear effects on EPS production, which resulted in either recovery or further decrease of hydraulic conductivity in the porous matrix. This non-linear response of biofilm to metal concentration could lead to different metal transport patterns in the long term. The concentration of metal contaminants plays a critical role in regulating the effect of metal–biofilm interaction. Our phenomenological study establishes linkages between chemical, microbial and physical processes of metal–biofilm interaction, and is an essential precursor to the development of models for this complex system. Specifically, these interactions are shown to be unpredictable, suggesting that more work needs to be done to constrain flow and transport parameters in biofilm-colonised porous media.