Metal Concentrations and Responses of Chironomid Larvae Exposed to Thailand Pulp and Paper Mill Effluent.

Pulp and paper mills (PPM) may discharge insufficiently treated waste into rivers and give rise to serious effects with aquatic life. This study investigated the biological response of the chironomid (Chironomus javanus, Kieffer) when exposed to PPM effluent. Effluent concentrations of BOD, COD, TKN, TS, Cr, Cu, Pb and Zn were high. Cd and Cr concentrations in chironomid were the most accumulated. Whole effluent toxicity on the chironomid test organism was significant as expressed by the percent survival and decreased with increasing concentration. Highest dry weight, head capsule and length of the chironomid test organism corresponded to 100% effluent at a specific time. Effect of dilution was assessed by using glutathione S-transferase activity on chironomid and corresponded to 6.25% effluent during 48-96 h which was significantly increased in the chironomid. The results showed that the chironomid was sensitive to PPM effluent and toxicity tests can be used for assessing the effect of effluent on aquatic species.

Nickel biopathways in tropical nickel hyperaccumulating trees from Sabah (Malaysia).

The extraordinary level of accumulation of nickel (Ni) in hyperaccumulator plants is a consequence of specific metal sequestering and transport mechanisms, and knowledge of these processes is critical for advancing an understanding of transition element metabolic regulation in these plants. The Ni biopathways were elucidated in three plant species, Phyllanthus balgooyi, Phyllanthus securinegioides (Phyllanthaceae) and Rinorea bengalensis (Violaceae), that occur in Sabah (Malaysia) on the Island of Borneo. This study showed that Ni is mainly concentrated in the phloem in roots and stems (up to 16.9% Ni in phloem sap in Phyllanthus balgooyi) in all three species. However, the species differ in their leaves - in P. balgooyi the highest Ni concentration is in the phloem, but in P. securinegioides and R. bengalensis in the epidermis and in the spongy mesophyll (R. bengalensis). The chemical speciation of Ni2+ does not substantially differ between the species nor between the plant tissues and transport fluids, and is unambiguously associated with citrate. This study combines ion microbeam (PIXE and RBS) and metabolomics techniques (GC-MS, LC-MS) with synchrotron methods (XAS) to overcome the drawbacks of the individual techniques to quantitatively determine Ni distribution and Ni2+ chemical speciation in hyperaccumulator plants.

In situ analysis of foliar zinc absorption and short-distance movement in fresh and hydrated leaves of tomato and citrus using synchrotron-based X-ray fluorescence microscopy.

BACKGROUND AND AIMS: Globally, zinc deficiency is one of the most important nutritional factors limiting crop yield and quality. Despite widespread use of foliar-applied zinc fertilizers, much remains unknown regarding the movement of zinc from the foliar surface into the vascular structure for translocation into other tissues and the key factors affecting this diffusion. METHODS: Using synchrotron-based X-ray fluorescence microscopy (µ-XRF), absorption of foliar-applied zinc nitrate or zinc hydroxide nitrate was examined in fresh leaves of tomato (Solanum lycopersicum) and citrus (Citrus reticulatus). KEY RESULTS: The foliar absorption of zinc increased concentrations in the underlying tissues by up to 600-fold in tomato but only up to 5-fold in citrus. The magnitude of this absorption was influenced by the form of zinc applied, the zinc status of the treated leaf and the leaf surface to which it was applied (abaxial or adaxial). Once the zinc had moved through the leaf surface it appeared to bind strongly, with limited further redistribution. Regardless of this, in these underlying tissues zinc moved into the lower-order veins, with concentrations 2- to 10-fold higher than in the adjacent tissues. However, even once in higher-order veins, the movement of zinc was still comparatively limited, with concentrations decreasing to levels similar to the background within 1-10 mm. CONCLUSIONS: The results advance our understanding of the factors that influence the efficacy of foliar zinc fertilizers and demonstrate the merits of an innovative methodology for studying foliar zinc translocation mechanisms.

Bioavailability and pharmacokinetics of arsenic are influenced by the presence of cadmium.

Mine wastes contain a mixture of metals and metalloids including arsenic (As) and cadmium (Cd). This study investigated the potential interaction between As and Cd in a rat model. Sprague Dawley rats were dosed with sodium arsenate via the oral (0, 0.5, 5 and 15 mg As kg(-1) b.w.) or intravenous (0.5 mg As kg(-1) b.w.) route to establish its dose-response relationship in terms of bioavailability and pharmacokinetic parameters. Bioavailability of As reduced when the dose of As increased. For the interaction study a fixed oral dose of As at 2.5 mg As kg(-1) b.w. solo and in combination with Cd as cadmium chloride at 3 or 6 mg Cd kg(-1) b.w. were administered to rats. Bioavailability of As was decreased by 34-35% in the presence of Cd. Elimination half-life of As was also decreased from 69 days in the As solo group to 13-22 days in the presence of 3 and 6 mg Cd kg(-1) b.w. respectively. Decreased urinary excretion of As and tissue accumulation were also observed. A probable explanation for these findings is that As co-administration with Cd could have resulted in the formation of less soluble cadmium-arsenic complexes in the guts of the rats. Nevertheless, such an interaction between As and Cd could only explained about 44-48% of the variation when mine waste materials containing both of these elements were administered to rats. This suggests other physical properties and chemical compound formation could contribute to the observed bioavailability of arsenic in complex environmental samples.

Interaction effects of lead on bioavailability and pharmacokinetics of arsenic in the rat.

Arsenic (As) and lead (Pb) are common contaminants found in mine waste materials. For an evidence-based risk assessment, it is important to better understand the potential interaction of mixed contaminants; and this interaction study was investigated in an in vivo rat model. Following co-administration of a fixed dose of As(V) as in sodium arsenate and different doses of Pb as lead acetate to Sprague-Dawley rats, blood arsenic concentration and bioavailability decreased. A decrease in As blood concentration when lead was co-administered was observed with increasing lead doses. Pharmacokinetic parameters for As in the blood showed faster absorption and elimination of this metalloid in the presence of Pb. The elimination half-life of As decreased from 67 days in As solo group to 27-30 with doses of Pb. Bioavailability of As was also decreased by 30-43 % in the presence of Pb. Decreased urinary excretion of Pb and tissue accumulation were also observed. It indicates lower absorption of As when co-administered with Pb. A probable explanation for these findings is that As co-administration with Pb could have resulted in the formation of less soluble lead arsenate. However, such an interaction between As and Pb could only explain about one-third of the variation when real mine waste materials containing both of these elements were administered to rats. This suggests that other effects from physical and chemical parameters could contribute to the bioavailability of arsenic in complex real environmental samples.

Dissolved organic carbon reduces uranium bioavailability and toxicity. 2. Uranium[VI] speciation and toxicity to three tropical freshwater organisms.

The influence of dissolved organic carbon (DOC) on the toxicity of uranium (U) to three Australian tropical freshwater species, the Northern Trout Gudgeon (Mogurnda mogurnda), green hydra (Hydra viridissima) and unicellular green alga (Chlorella sp.) was assessed. Exposures were conducted in synthetic soft water without DOC and with DOC added in the form of standard Suwannee River Fulvic Acid (SRFA). Organisms were exposed to a range of U concentrations at a range of DOC concentrations (0-20 mg L(-1)). U toxicity was up to 20 times less in water containing 20 mg L(-1) DOC, relative to DOC-free test waters. U toxicity was also assessed using natural water from a tropical Australian billabong containing 10 mg L(-1) DOC. U toxicity was up to ten times less in the billabong water, relative to DOC--free test waters. SRFA was twice as effective at reducing U toxicity as the billabong water at equivalent DOC concentrations. Geochemical speciation modeling confirmed the decreased U toxicity that resulted from both DOC sources was primarily due to a decrease in the free uranyl ion (UO2(2+)) through complexation with DOC. A predictive model is presented for each of the organisms that can be used to predict U toxicity at a given U and DOC concentration.

Consistent chemical form of Cd in liver and kidney tissues in rats dosed with a range of Cd treatments: XAS of intact tissues.

X-ray absorption spectroscopy of frozen intact tissues shows that in rats exposed to a range of treatments involving cadmium, alone or in combination with other metal ions, the coordination environment of cadmium is consistent in both the liver and kidney. Comparison of the spectra from the rat tissues to biologically relevant model compounds indicates that the vast majority of the cadmium is bound to metallothionein in these tissues.

Effects of residues from municipal solid waste landfill on corn yield and heavy metal content.

The effects of residues from municipal solid waste landfill, Khon Kaen Municipality, Thailand, on corn (Zea mays L.) yield and heavy metal content were studied. Field experiments with randomized complete block design with five treatments (0, 20, 40, 60 and 80% v/v of residues and soil) and four replications were carried out. Corn yield and heavy metal contents in corn grain were analyzed. Corn yield increased by 50, 72, 85 and 71% at 20, 40, 60 and 80% treatments as compared to the control, respectively. All heavy metals content, except cadmium, nickel and zinc, in corn grain were not significantly different from the control. Arsenic, cadmium and zinc in corn grain were strongly positively correlated with concentrations in soil. The heavy metal content in corn grain was within regulated limits for human consumption.

Silica reduces the toxicity of aluminium to a tropical freshwater fish (Mogurnda mogurnda).

The toxicity of aluminium (Al) to fish in acidic waters has been well documented. It was therefore expected that Al toxicity would be significant in fish communities in Gadjarrigamarndah (Gadji) Creek, a seasonally flowing stream in tropical northern Australia. This creek receives acidic groundwater containing elevated concentrations of Al from earlier land irrigation of treated mine tailings water from the former Nabarlek uranium mine. It was hypothesised that Al toxicity was reduced by high levels of silica (Si) in the water, and the subsequent formation of Al-silicate complexes. This prompted a laboratory assessment of the toxicity of Gadji Creek water to sac-fry of the native fish, Mogurnda mogurnda, followed by more detailed investigation of the toxicity of Al and the influence of Si in reducing Al toxicity. No mortality of M. mogurnda sac-fry was observed in two toxicity tests using Gadji Creek water collected in August 1997 and September 1998. The majority of Al (80-95%) was calculated to be complexed with humic substances and sulfate, with < 1% being complexed with silicate. Assessment of the influence of silica on the acute toxicity of Al in the absence of natural organic complexants (i.e. in reconstituted freshwater, pH 5) revealed that Si reduced Al toxicity. As the molar ratio of Si:Al was increased, the percent survival of M. mogurnda sac-fry increased until there was no significant (P > 0.05) difference from the controls. However, speciation modelling again predicted that little (< 3%) Al complexed with silicate, with the speciation and bioavailability of Al remaining constant as the molar ratio of Si:Al increased. Therefore, the original hypothesis that Al-silicate complexes in solution reduced the toxicity of Al to M. mogurnda could not be supported. This potential mechanism, and an alternative hypothesis, that Si competes with Al for binding sites at the fish gill surface, requires further investigation.