Metal accumulation in the smooth toadfish, Tetractenos glaber, in estuaries around Sydney, Australia

This study determined the metal levels in sediments and tissues of a common estuarine fish, Tetractenos glaber (smooth toadfish), from two metal contaminated and two reference estuaries near Sydney, Australia. Metal levels were highest in sediments and fish from contaminated estuaries. Gonads contained the highest metal levels followed by muscle, gill and liver. Metal accumulation was gender-dependant (e.g. male gonads were >20 times higher in As than females; female gills were >30 times higher than males for Pb). Cadmium, Pb and Ni levels in fish tissues reflected sediment levels, indicating sediment and/or dietary metal uptake. Levels of As, Co, Cd & Pb in gills showed similar patterns to other tissues, suggesting that metals may have been taken up by gills through contaminated water. Similar metal patterns in tissues and sediments suggest more than one uptake pathway. This study indicates that multiple factors influence metal accumulation in fish.     

Metal accumulation in the greentail prawn, Metapenaeus bennettae, in Sydney and Port Hacking estuaries, Australia

Metal concentrations of the inshore greentail prawn, Metapenaeus bennettae, and surface sediments from locations within Sydney estuary and Port Hacking (Australia) were assessed for bioaccumulation and contamination. The current study aimed to assess metal concentrations in prawn tissue (tail muscle, exoskeleton, hepatopancreas and gills), relate whole body prawn tissue metal concentrations to sediment metal concentrations and animal size, as well as assess prawn consumption as a risk to human health. Metal concentrations were highest in sediment and prawns from contaminated locations (Iron Cove, Hen and Chicken Bay and Lane Cove) in Sydney estuary compared with the reference estuary (Port Hacking). Concentrations in sediments varied considerably between sites and between metals (As, Cd, Cr, Cu, Ni, Pb and Zn), and although concentrations exceeded Interim Sediment Quality Guideline-Low values, metals (As, Cd, Cr, Cu, Ni, Pb and Zn) were below Australian National Health and Medical Research Council human consumption guidelines in prawn tail muscle tissue. Metal concentrations in prawn tail muscle tissue were significantly different (p?≤?0.05) amongst locations for Pb, Zn and Cd, and metal concentrations were generally highest in gills tissue, followed by the hepatopancreas, exoskeleton and tail muscle. The exoskeleton contained the highest Sr concentration; the hepatopancreas contained the highest As, Cu and Mo concentrations; and the gills contained the highest Al, Cr, Fe and Pb concentrations. Concentrations of Pb, As and Sr were significantly different (p?≤?0.05) between size groups amongst locations.     

Trace metals and organochlorines in sediments near a major ocean outfall on a high energy continental margin (Sydney, Australia)

Sewage effluent from a large ocean outfall south of Sydney, southeastern Australia, is efficiently dispersed on this high energy continental margin. An enrichment of Ag, Cu, Pb and Zn is only detectable in the fine fraction (<62.5 microm) of sediment. Ag, Co, Cu, Ni, Pb and Zn in the bulk sample correlate strongly with the mud content of surficial sediment, making an identification of the anthropogenic trace metal source difficult using total sediment analyses. The concentrations of HCB and DDE in the total sediment are also slightly elevated near the outfall. In the vicinity of the outfall, the estimated sewage component in the fine fraction of sediment, using Ag, Cu and Zn in a conservative, two-endmember physical mixing model, is <5% and is <0.25% of the total sediment. A greater anthropogenic Pb component in the fine fraction (mean: 24.8%) of surficial sediment compared to Ag, Cu and Zn may suggest a source other than sewage to Sydney continental margin sediments.     

On-road ultrafine particle concentration in the M5 East road tunnel,Sydney, Australia

The human health effects following exposure to ultrafine (<100 nm) particles (UFPs) produced by fuel combustion, while not completely understood, are generally regarded as detrimental. Road tunnels have emerged as locations where maximum exposure to these particles may occur for the vehicle occupants using them. This study aimed to quantify and investigate the determinants of UFP concentrations in the 4 km twin-bore (eastbound and westbound) M5 East tunnel in Sydney, Australia. Sampling was undertaken using a condensation particle counter (CPC) mounted in a vehicle traversing both tunnel bores at various times of day from May through July, 2006. Supplementary measurements were conducted in February, 2008. Over three hundred transects of the tunnel were performed, and these were distributed evenly between the bores. Additional comparative measurements were conducted on a mixed route comprising major roads and shorter tunnels, all within Sydney. Individual trip average UFP concentrations in the M5 East tunnel bores ranged from 5.53 × 10⁴ p cm^?3 to 5.95 × 10⁶ p cm^?3. Data were sorted by hour of capture, and hourly median trip average (HMA) UFP concentrations ranged from 7.81 × 10⁴ p cm^?3 to 1.73 × 10⁶ p cm^?3. Hourly median UFP concentrations measured on the mixed route were between 3.71 × 10⁴ p cm^?3 and 1.55 × 10⁵ p cm^?3. Hourly heavy diesel vehicle (HDV) traffic volume was a very good determinant of UFP concentration in the eastbound tunnel bore (R² = 0.87), but much less so in the westbound bore (R² = 0.26). In both bores, the volume of passenger vehicles (i.e. unleaded gasoline-powered vehicles) was a significantly poorer determinant of particle concentration. When compared with similar studies reported previously, the measurements described here were among the highest recorded concentrations, which further highlights the contribution road tunnels may make to the overall UFP exposure of vehicle occupants.     

The use of sedimentary metal data in predictive modelling of estuarine contamination,assessment of environmental condition and pollutant source identification (Narrabeen Lagoon,Sydney, Australia)

Environmental Science and Pollution Research - Narrabeen Lagoon is recognized as an Intermittently Closed and Open Lake or Lagoon (ICOLL) and is the largest coastal lagoon (2.2&nbsp;km2) in the...     

Use of sedimentary metals to predict metal concentrations in black mussel (Mytilus galloprovincialis) tissue and risk to human health (Sydney estuary, Australia)

Filter-feeding bivalves have been used extensively as an indicator of ecosystem condition and in management of estuarine environments. The current study aimed to determine whether sedimentary metals could predict metal concentrations in tissue of filter-feeding mussels (Mytilus galloprovincialis) and to identify areas of the estuary where mussel consumption posed a human health risk. Mussel tissue Cu and Zn concentrations (wet weight) were below guideline values for human consumption in all parts of the waterway, whereas Pb tissue concentrations exceed these guidelines (2.0 μg?g^?1 wet weight) in the upper reaches of some embayments of the estuary. Concentrations of Cu and Pb in the fine fraction (<62.5 μm) of bottom sediment reasonably predicted concentrations (dry weight) of these metals in mussel tissue (r ²?=?0.460 and p?=?0.001 and r ²?=?0.669 and p?<?0.0001, respectively) as these materials are resuspendable and available to filter-feeding estuarine animals, whereas total sediment and mussel tissue were poorly related. Lead concentrations (>350 μg?g^?1) in fine sediments indicated areas of this estuary where human health was at risk due to high tissue concentrations of this metal. These results give encouragement for the use of the metal concentration in fine sediments as an indicator of estuarine condition and risk to human health in this waterway. Mussels were distributed in all parts of the estuary, even in areas where metal concentrations exceeded sediment quality guidelines.     

Concentrations and spatial distribution of trace metals in mangrove sediments from the Brisbane River, Australia

Fifty surface sediment samples were collected from 12 transects through a mangrove woodland near the mouth of the Brisbane River, Australia. Samples were analyzed for 10 trace metals; measured concentrations (microg g(-1)) were: Cu 3.1-34.1; Pb 7.7-84.7; Zn 40.8-144.0; Ag nd-2.8; Cr 7.6-116.8; V 16.4-57.9; Mo 7.6-82.6; Ni 2.4-57.6; As nd-13.0; and Cd nd-2.0. Coefficients of variation ranged from 22-153%. Sediments were moderately contaminated, with Mo being enriched by up to thirty times background levels. Spatial variation was considerable, and canonical trend analysis showed concentrations of all metals but Ag and Cr tended to increase downshore, suggesting tidal deposition was important in determining metal concentrations. Silver and Cr concentrations appeared to be a consequence of contamination from landward point sources. An investigation of different random sampling intensities showed the spatial variation required that many samples be taken for a satisfactory assessment of metal burdens. Even so, mean values were not a good indication of the possible environmental effects of the metal contamination. Since metal concentrations increase downshore in inter-tidal environments, a more appropriate sampling strategy would be to take a downshore series of samples normal to the shoreline.     

养护条件对二次铝灰-垃圾飞灰基地聚物中重金属稳固化的影响

以添加SiO2粉末后的二次铝灰和垃圾焚烧飞灰为原料,经过碱激发制备地聚物固化体。将制备好的地聚物固化体样品分别放在30、35、40、45和50 ℃,相对湿度为80%的恒温恒湿培养箱内养护,探究不同养护条件对固化体中重金属浸出特性的影响,并考察生活垃圾焚烧飞灰处理前后重金属化学形态、晶体结构和微观形貌的改变。结果表明：重金属Cr的相对浸出率在30～45 ℃下降明显,45～50 ℃内趋于平缓;而Cd和Pb的相对浸出率在30～40 ℃略微上升,40～50 ℃呈下降趋势,并且Pb的相对浸出率在40～45 ℃下降明显;Zn的相对浸出率随着养护温度的升高缓慢下降。重金属Cr、Cd、Zn和Pb的相对浸出率在前10 d内下降较大,10～14 d下降缓慢。当养护温度为50 ℃时,地聚物中重金属Cr、Cd、Zn和Pb的浸出浓度分别降到0.172、0.072、0.218和3.803 mg·L-1,满足《生活垃圾填埋场控制标准》（GB 16889-2008）的浸出要求。     

Bioavailability, accumulation and effects of heavy metals in sediments with special reference to United Kingdom estuaries: a review

Using mainly United Kingdom estuaries as examples, various factors governing the bioavailability, bioaccumulation and biological effects of heavy metals in sediment-dominated estuaries are reviewed. Estuaries and metals primarily discussed include the Mersey (Hg, methylmercury; Pb, alkyllead), the Loughor (Cr, Sn), the Severn (Ag, Cd), the Fal (As, Cu, Sn, Zn), Poole Harbour (Cd, Hg, Se, tributyltin) and Southampton Water (tributyltin). Concentrations and bioavailabilities of metals in estuarine sediments depend on many different processes. Examples include (1) mobilisation of metals to the interstitial water and their chemical speciation, (2) transformation (e.g. methylation) of metals including As, Hg, Pb and Sn (3) the control exerted by major sediment components (e.g. oxides of Fe and organics) to which metals are preferentially bound, (4) competition between sediment metals (e.g. Cu and Ag; Zn and Cd) for uptake sites in organisms, and (5) the influence of bioturbation, salinity, redox or pH on these processes. Under field conditions, identification of dominant processes can be achieved by observing the goodness of fit between metal concentrations in ubiquitous deposit-feeding species and levels in various types of sediment extract over a wide spectrum of sediment types. Factors of more local importance are often indicated by the marked deviation of some points from otherwise excellent relationships. For example, points lying above the line relating tissue Sn concentrations in the clam Scrobicularia plana to those in 1 n HCl extracts of sediments were found to reflect the accumulation of tributyltin, a more readily bioavailable form of Sn. In the same species, unexpectedly high tissue-Cu concentrations were characteristic of very anoxic in sediments and tissue And As and Pb concentrations were suppressed in sediments having high concentrations of Fe oxides. Under field conditions, examples of deleterious effects on benthic organisms that can be attributed to specific metallic pollutants are comparatively rare. Effects of tributyltins from antifouling paints on oysters and neogastropods have been documented and their toxicity has undoubtedly led to environmental degradation in many UK estuaries and coastal areas. In estuaries contaminated with metal-mining wastes, the effects of Cu and Zn on species distribution can be observed, but they are generally less obvious than would be predicted from experimental data. Effects are ameliorated by the induction of metal tolerance mechanisms in some species and in others by the appearance of tolerant strains. The induction of metal detoxification systems involving the formation of granules or metal-binding proteins leads in some species to tissue concentrations that are orders of magnitude higher than normal. For example, high concentrations of Cd and Ag have been found in some species from the Severn Estuary, although there is no unequivocal evidence that either metal has caused deleterious effects on benthic populations. On the other hand, experimental studies with Ag, Cd, Cr, Cu, Hg and Zn show that they are toxic to some species at environmentally realistic levels. Since pollutants rarely occur singly, it is likely that in many moderately contaminated estuaries metals contribute to the stress to organisms caused by substances requiring detoxification. There has been much speculation over the years concerning the biomagnification of metals with increasing trophic levels along food chains. Whilst animals having higher metal concentrations than their prey are sometimes found, the only consistent evidence of biomagnification concerns methylmercury. When estuarine birds are considered, there are relatively few instances in which deleterious effects can unequivocally be attributed to metals or their compounds. However, the Mersey bird kill was attributable to alkyllead pollution from industry. Among other organometals, methylmercury has proved toxic to birds but, so far, no evidence for the toxicity of tributyltin has been reported. However, the compound may have affected bird populations through its effects on the abundance of prey organisms, particularly estuarine molluscs. Of the inorganic forms of metals, Pb in the form of shot has caused problems in many areas and Cd, Hg and Se are suspected of causing toxic effects. There is little field evidence that birds have been affected by Ag, As, Cr, Cu or Zn individually. On the other hand, it is difficult to exclude the possibility that, additively, these metals may produce a significant effect. In part, the lack of evidence reflects the fact that relatively little research has been done. There is scope for more work on metals and organometals in estuarine birds, particularly with regard to their metabolism and their effects on juveniles and individuals subjected to stresses such as starvation.     

Effects of sediment quality on macroinvertebrates in the Sunraysia region of the Murray-Darling Rivers, Australia

A field-based microcosm approach was tested to identify deterioration of sediment quality in waterways using freshwater macroinvertebrates. The method can potentially identify the nature of contaminants based on species-specific responses. Sediments were collected from the Murray and Darling Rivers and irrigation drains within the Sunraysia region of south-eastern Australia and compared to non-polluted reference sediment. Clean sediments were also spiked with fertiliser to test whether nutrients affected the aquatic fauna. Seven of the eight sediments from the Sunraysia region had a negative impact on the macroinvertebrates, in particular sediment from the Darling River, which supported an impoverished fauna. Three species of chironomid showed varied responses to sediment quality and, although it was hypothesised that nutrients may have impacted on the macroinvertebrate fauna, the results suggest that other pollutants are also involved. The field-based microcosm method proved effective for determining the impact of sediment quality on indigenous macroinvertebrates.     

Relationships between hepatic trace element concentrations, reproductive status, and body condition of female greater scaup

We collected female greater scaup (Aythya marila) on the Yukon-Kuskokwim Delta, Alaska during two breeding seasons to determine if concentrations of 18 trace elements in livers and eggs were elevated and if hepatic concentrations correlated with body condition or affected reproductive status. Fifty-six percent, 5%, and 42% of females, respectively, had elevated hepatic cadmium (Cd: >3 μg g⁻¹ dry weight [dw]), mercury (Hg: >3 μg g⁻¹ dw), and selenium (Se: >10 μg g⁻¹ dw). Somatic protein and lipid reserves were not correlated with hepatic Cd or Hg, but there was a weak negative correlation between protein and Se. Hepatic Cd, Hg, and Se were similar in females that had and had not initiated egg production. In a sample of six eggs, 33% and 100%, respectively, contained Se and Hg, but concentrations were below embryotoxicity thresholds. We conclude that trace element concentrations documented likely were not adversely impacting this study population.     

The dispersal and storage of sediment-associated metals in an arid river system: the Leichhardt River, Mount Isa, Queensland, Australia

This paper details the distribution of Cu, Pb and Zn in aquatic systems draining Mount Isa Ag-Cu-Pb-Zn Mine in arid northern Queensland, Australia. Sediment-metal concentrations in the <2mm grain-size fraction adjacent to and downstream of the mine significantly exceed background concentrations (Cu, 159; Pb, 36; Zn, 86 ppm) as well as Australian government sediment quality low trigger guidelines (Cu, 65; Pb, 50; Zn, 200 ppm). Overbank sediments are more contaminated than channel sediments with mean values of Cu, 480; Pb, 540; Zn, 750 ppm. Mean concentrations in cut riverbank samples from the <2mm fraction were Cu, 195; Pb, 724; Zn, 807 ppm. Corresponding <180 microm samples returned concentrations of Cu, 321; Pb, 995; Zn, 1110 ppm. Delivery of contaminants during wet seasons from Mount Isa Mine and historically contaminated riverbanks remains an ongoing issue. The ease of dust entrainment in arid zones means that sediments enriched in toxic concentrations of metals may be widely dispersed and ultimately ingested and absorbed by biota.     

灯心草部分生理生化指标对土壤复合重金属胁迫的响应

通过盆栽试验,以叶绿素含量和POD、SOD、CAT3种抗氧化酶活性作为观测指标,研究了Cu、Cd、Pb、Zn和As复合重金属胁迫下灯心草部分生理生化指标的变化趋势和机理.结果表明,灯心草的生理毒害效应呈明显的剂量-效应关系.表现为与对照相比,叶绿素含量减少,叶绿素a/b值降低,叶片失绿现象明显.随着复合重金属胁迫浓度的增加,灯心草3种酶活性均呈先升后降的变化趋势,但出现抗性酶活性高峰所对应的重金属浓度不同,表现出不同的特征变化趋势.总体来说,在接近土壤环境质量标准低浓度设计范围内,酶活性有逐渐被激活的趋势.但在高浓度水平下,酶活性普遍受到抑制.生长在铅锌尾矿和模拟矿毒水污染土壤中的灯心草叶绿素合成受到显著抑制(P＜0.05),但POD和CAT两种酶活性均高于对照.     

Effects of Heavy metals on plants and resistance mechanisms

GOAL, SCOPE AND BACKGROUND: As one of the consequences of heavy metal pollution in soil, water and air, plants are contaminated by heavy metals in some parts of China. To understand the effects of heavy metals upon plants and the resistance mechanisms, would make it possible to use plants for cleaning and remediating heavy metal-polluted sites. METHODS: The research results on the effects of heavy metals on plants and resistant mechanisms are compiled from Chinese publications from scientific journals and university journals, mostly published during the last decade. RESULTS AND DISCUSSION: Effects of heavy metals on plants result in growth inhibition, structure damage, a decline of physiological and biochemical activities as well as of the function of plants. The effects and bioavailability of heavy metals depend on many factors, such as environmental conditions, pH, species of element, organic substances of the media and fertilization, plant species. But, there are also studies on plant resistance mechanisms to protect plants against the toxic effects of heavy metals such as combining heavy metals by proteins and expressing of detoxifying enzyme and nucleic acid, these mechanisms are integrated to protect the plants against injury by heavy metals. CONCLUSIONS: There are two aspects on the interaction of plants and heavy metals. On one hand, heavy metals show negative effects on plants. On the other hand, plants have their own resistance mechanisms against toxic effects and for detoxifying heavy metal pollution. RECOMMENDATIONS AND OUTLOOK: To study the effects of heavy metals on plants and mechanisms of resistance, one must select crop cultivars and/or plants for removing heavy metals from soil and water. More highly resistant plants can be selected especially for a remediation of the pollution site. The molecular mechanisms of resistance of plants to heavy metals should be studied further to develop the actual resistance of these plants to heavy metals. Understanding the bioavailability of heavy metals is advantageous for plant cultivation and phytoremediation. Decrease in the bioavailability to farmlands would reduce the accumulation of heavy metals in food. Alternatively, one could increase the bioavailability of plants to extract more heavy metals.     

Effects of phosphorothionate on the reproductive system of male rats

Acute and Sub-acute toxic effects of a new pesticide phosphorothionate coded as RPR-V on testis of albino rat were studied. For the acute study, rats received a single dose of 30 mg/kg of RPR-V and sacrificed after 24 hours. For the Subacute study, 1.42 mg/kg/day was administered orally to rats for 10 days and 21 days. Acute exposure of rats to RPR-V brought no change either in the Gonadosomatic Index (GSI) or in the structure of testis or in the serum levels of Testosterone. Similarly, no significant change was observed in the Glutathione S-transferase (GST) activity. But, in testis there was significant increased in the reduced Glutathione (GSH) and Acid Phosphatase (AcP), whereas Alkaline Phosphatase (AkP) levels decreased significantly at 24hr post treatment. On 7th day (withdrawal period) after the cessation of the treatment the GSH, AcP, and AkP levels reached to near control. The sub-acute study revealed a significant post treatment. Due to RPR-V treatment the testis AcP levels increased significantly at 21st day of medication but AkP levels decreased both at 10th and 21st day of post treatment. Histopathological studies showed that after 10th day testis showed considerable loss of spermatozoids and at 21st day complete derangement of cellular organization was observed. Testosterone levels decreased significantly after 10th day and remained significantly low at 21st day. However, withdrawal studies showed a recovery in testis of rat treated with RPR-V. GST, GSH, GSI, AcP and AkP values were recovered, testosterone levels were also recovered but recovery in testis structure remained at a low profile.     

Effects of heavy metals on population growth and metallothionein gene expression in the mosquito Culex quinquefasciatus, from Calcutta, India

Major water bodies in and around the city of Calcutta (India) receive heavy metal contaminated effluents from industries, households, and vehicular traffic through sewage or drainage. We quantified concentrations of Cu, Zn, and Cd from three water bodies at Kalighat, Tangra, and VIP Road, respectively. The concentrations of these heavy metals were significantly greater in the summer than in monsoon when heavy downpours resulted in reduced metal concentrations. Concentrations of metals in the mosquito Culex quinquefasciatus also reflected such seasonal fluctuations. Hatchability and survivorship of C. quinquefasciatus significantly differed among the sites and were reduced significantly from the control. Exposure to heavy metals also induced MT-gene expression in C. quinquefasciatus, likely helping them to survive in the water bodies stressed with heavy metals. MT-gene activity demonstrated significant variation among sites and seasons with the highest activity in the summer in the VIP Road population. This study suggests that C. quinquefasciatus could be used as an ecological indicator of heavy metal pollution by monitoring its MT-gene expression.     

Effects of salinity, DOM and metals on the fate and microbial toxicology of propetamphos formulations in river and estuarine sediment

Toxicity studies tend to use pure pesticides with single organisms. However, natural systems are complex and biological communities diverse. The organophosphate pesticide propetamphos (PPT) has been found exceeding regulatory limits (100 ng L⁻¹) in rivers. We address whether solution properties affect the fate of Analar (Analar-PPT) or industrial PPT (PPT-Ind) propetamphos formulations and whether propetamphos and metal toxicant effects are additive, antagonistic or synergistic? The sorption, desorption, biodegradation and microbial toxicology of Analar-PPT and PPT-Ind were investigated in Conwy River and estuary sediment. Results showed elevated salinity enhanced PPT sorption, while higher salinities increased PPT-Ind retention. Higher dissolved organic matter (DOM) and low salinity slowed Analar-PPT biodegradation (1.9 × 10⁻³ h⁻¹). Analar-PPT and PPT-Ind biodegradation was further reduced by low salinity, high DOM and dissolved Zn and Pb (6.3 × 10⁻⁴ h⁻¹, 1100 h t_½ for Analar-PPT; 7.5 × 10⁻⁴ h⁻¹, 924 h t_½ for PPT-Ind). Toxicity effects of PPT, Zn and Pb in equitoxic ratio were higher for PPT-Ind (4.7 μg PPT-Ind g⁻¹; 581 μg Zn g⁻¹; 395 μg Pb g⁻¹) than for Analar-PPT (34.6 μg PPT g⁻¹; 312 μg Zn g⁻¹; 212 μg Pb g⁻¹) whilst a toxicant ratio 1:100:10 suggested small quantities of Analar-PPT (EC₁₀ = 0.06 μg g⁻¹) affected microbial communities. The combined toxicity effect was more than additive. Thus, industrial formulations and pollutant mixtures should be considered when assessing environmental toxicity.     

Effects of sewage effluent discharge on the abundance, condition and mortality of hulafish, Trachinops taeniatus (Plesiopidae)

The effects of sewage effluent on the abundance, condition (length and reproduction) and mortality of hulafish Trachinops taeniatus were investigated at multiple outfall and control locations on the central coast of New South Wales, Australia. Underwater visual surveys found consistently fewer T. taeniatus at locations where sewage was discharged compared to control locations. The condition of T. taeniatus was investigated by comparing mean length and reproductive indices of fish from two outfall and two control locations. Fish from the largest outfall location were significantly smaller in comparison with fish from control locations. Gravid female fish from outfall locations had similar gonadosomatic indices but a significantly greater number of eggs and smaller size of eggs in comparison with fish from control locations. Mortality of T. taeniatus was investigated during 2-week, in situ, caging experiments at multiple locations and times and 80% of fish survived, although mortalities of up to 73% per cage were recorded at one sewage outfall. T. taeniatus may be a suitable environmental indicator species of sewage pollution.     

Quantitative assessment of the toxic effects of heavy metals on 1,2-dichloroethane biodegradation in co-contaminated soil under aerobic condition

1,2-Dichloroethane (1,2-DCA) is one of the most hazardous pollutant of soil and groundwater, and is produced in excess of 5.44 × 10⁹ kg annually. Owing to their toxicity, persistence and potential for bioaccumulation, there is a growing interest in technologies for their removal. Heavy metals are known to be toxic to soil microorganisms at high concentrations and can hinder the biodegradation of organic contaminants. In this study, the inhibitory effect of heavy metals, namely; arsenic, cadmium, mercury and lead, on the aerobic biodegradation of 1,2-DCA by autochthonous microorganisms was evaluated in soil microcosm setting. The presence of heavy metals was observed to have a negative impact on the biodegradation of 1,2-DCA in both soil samples tested, with the toxic effect being more pronounced in loam soil, than in clay soil. Generally, 75 ppm As³⁺, 840 ppm Hg²⁺, and 420 ppm Pb²⁺ resulted in 34.24%, 40.64%, and 45.94% increase in the half live (t_½) of 1,2-DCA, respectively, in loam soil, while concentrations above 127.5 ppm Cd²⁺, 840 ppm Hg²⁺ and 420 ppm of Pb²⁺ and less than 75 ppm As³⁺ was required to cause a >10% increase in the t_½ of 1,2-DCA in clay soil. A dose-dependent relationship between degradation rate constant (k₁) of 1,2-DCA and metal ion concentrations was observed for all the heavy metals tested, except for Hg²⁺. This study demonstrated that different heavy metals have different impacts on the degree of 1,2-DCA degradation. Results also suggest that the degree of inhibition is metal specific and is also dependent on several factors including; soil type, pH, moisture content and available nutrients.     

Effects of oxygen on the release and distribution of phosphorus in the sediments under the light condition

Effects of oxygen on the release and distribution of phosphorus (P) in the sediments in the presence of light were investigated, using sediment cores and overlying water from Lake Taihu, in China. The results show that P can be released from sediments to the overlying water in both anoxic and aerobic conditions. But more P was released in the anoxic condition. The transformation of P between various fractions in the sediments was observed during the release experiments. Concentrations of Ca-bound P and organic P in the sediments decreased in both conditions, but Fe/Al-bound P increased in the aerobic condition. The decrease of total P and P fractions in the sediments is consistent with the accumulative increase in quantity (AIQ) of total P (TP) in the overlying water, but is contrary with the AIQ of dissolved inorganic P. This is due to the uptake of algae by the dissolved inorganic P. Total nitrogen in the sediments in the anoxic condition was lower than that in the aerobic condition, and pH in the overlying water increased in the anoxic condition.