Dietary exposure to heavy metals is a matter of concern for human health risk through the consumption of rice, vegetables and other major foodstuffs. In the present study, we investigated ...concentrations of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) in Australian grown and imported rice and vegetables on sale in Australia. The mean concentrations of Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn in Australian grown rice were 7.5µgkg−1, 21µgkg−1, 144µgkg−1, 2.9mgkg−1, 24.4mgkg−1, 166µgkg−1, 375µgkg−1, and 17.1mgkg−1 dry weight (d. wt.), respectively. Except Cd, heavy metal concentrations in Australian grown rice were higher than Bangladeshi rice on sale in Australia. However, the concentrations of Cd, Cr, Cu, and Ni in Indian rice on sale in Australia were higher than Australian grown rice. The concentrations of Cu and Ni in Vietnamese rice, and that of Cd, Cr, Cu, Ni, and Pb in Thai rice on sale in Australia were also higher than Australian grown rice. Heavy metal concentrations in Pakistani rice on sale in Australia were substantially lower than that in Australian grown rice. In Australian grown rice varieties, the concentrations of heavy metals were considerably higher in brown rice varieties than white rice varieties, indicating Australian brown rice as a potential source of dietary heavy metals for Australian consumers. The mean concentrations of heavy metals in Australian grown and Bangladeshi vegetables on sale in Australia were also determined. Some of the Australian grown and Bangladeshi vegetables contained heavy metals higher than Australian standard maximum limits indicating them as potential sources of dietary heavy metals for Australian consumers. Further investigation is required to estimate health risks of heavy metals from rice and vegetables consumption for Australian consumers.
Display omitted Concentrations of heavy metals (Cd, Co, Cr, Pb, Ni, Mn, Cu and Zn) in Australian grown rice.
•Except Cd, heavy metals in Australian rice were higher than Bangladeshi rice on sale in Australia.•Concentrations of Cd, Cr, Cu and Ni were higher in Indian and Thai rice than in Australian rice.•Heavy metals in Australian grown and Bangladeshi vegetables on sale in Australia were comparable.•Some of the rice and vegetables contained heavy metals higher than Australian standard maximum limit indicating a health risk for the consumers.
The survival of aquatic biota in stream ecosystems depends on both water quantity and quality, and is particularly susceptible to degraded water quality in regulated rivers. Maintenance of ...environmental flows (e-flows) for aquatic biota with optimum water quantity and quality is essential for sustainable ecosystem services, especially in developing regions with insufficient stream monitoring of hydrology, water quality and aquatic biota. Few e-flow methods are available that closely link aquatic biota tolerances to pollutant concentrations in a simple and practical manner. In this paper a new method was proposed to assess e-flows that aimed to satisfy the requirements of aquatic biota for both the quantity and quality of the streamflow by linking fish tolerances to water quality criteria, or the allowable concentration of pollutants. For better operation of water projects and control of pollutants discharged into streams, this paper presented two coefficients for streamflow adjustment and pollutant control. Assessment of e-flows in the Wei River, the largest tributary of the Yellow River, shows that streamflow in dry seasons failed to meet e-flow requirements. Pollutant influx exerted a large pressure on the aquatic ecosystem, with pollutant concentrations much higher than that of the fish tolerance thresholds. We found that both flow velocity and water temperature exerted great influences on the pollutant degradation rate. Flow velocity had a much greater influence on pollutant degradation than did the standard deviation of flow velocity. This study provides new methods to closely link the tolerance of aquatic biota to water quality criteria for e-flow assessment. The recommended coefficients for streamflow adjustment and pollutant control, to dynamically regulate streamflow and control pollutant discharge, are helpful for river management and ecosystems rehabilitation. The relatively low data requirement also makes the method easy to use efficiently in developing regions, and thus this study has significant implications for managing flows in polluted and regulated rivers worldwide.
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•We present a new e-flows assessment method linking fish tolerances to pollutant criteria.•Requirements of fish for both quantity and quality of streamflow were well addressed.•The method is not data-intensive especially suitable for data-scarce rivers.•It provides new ways to link tolerance of aquatic biota to water quality concentrations.•It has significant implications for managing flows in polluted, regulated rivers worldwide.
The breakdown of allochthonous organic matter, is a central step in nutrient cycling in stream ecosystems. There is concern that increased temperatures from climate change will alter the breakdown ...rate of organic matter, with important consequences for the ecosystem functioning of alpine streams. This study investigated the rate of leaf litter breakdown and how temperature and other factors such as microbial and invertebrate activities influenced this over elevational and temporal gradients. Dried leaves of Snow Gum (Eucalyptus pauciflora) and cotton strips were deployed in coarse (6 mm), and fine (50 μm) mesh size bags along an 820 m elevation gradient. Loss of mass in leaf litter and cotton tensile strength per day (k per day), fungal biomass measured as ergosterol concentration, invertebrate colonization of leaf litter, and benthic organic matter (mass and composition) were determined. Both microbial and macroinvertebrate activities were equally important in leaf litter breakdown with the abundance of shredder invertebrate taxa. The overall leaf litter breakdown rate and loss of tensile strength in cotton strips (both k per day) were greater during warmer deployment periods and at lower elevations, with significant positive relationships between mean water temperature and leaf breakdown and loss of tensile strength rate, but no differences between sites, after accounting for the effects of temperature. Despite considerably lower amounts of benthic organic matter in streams above the tree line relative to those below, shredders were present in coarse mesh bags at all sites. Ergosterol concentration was greater on leaves in coarse mesh bags than in fine mesh bags, implying differences in the microbial communities. The importance of water temperatures on the rate of leaf litter breakdown suggests the potential effects of climate change‐induced temperature increases on ecological processes in such streams.
We aimed at understanding how spatial and temporal water temperatures influenced AOM breakdown in alpine streams. Microbial and macroinvertebrate activities were monitored and showed to be elevated at lower elevations and during warmer periods. Climate change induced warming will therefore potentially change alpine stream ecosystem, standing biomass and promote increased nutrient cycling through AOM breakdown.
Rice is an important route of arsenic (As) exposure to humans, especially populations with rice-based diets. Human health risk of As varies greatly with rice variety and country of origin. The ...purpose of the present study was to determine total and speciated As in Australian-grown and imported rice on sale in Australia to assess their health risk to consumers. The total As (tAs) concentrations in Australian-grown organic brown, medium grain brown, and organic white rice were 438 ± 23, 287 ± 03, and 283 ± 18 μg kg–1 dry weight (d wt), respectively. In Bangladeshi, Indian, Pakistani, and Thai rice imported and on sale in Australia, tAs concentrations were 56 ± 05, 92 ± 10, 82 ± 06 and 172 ± 24 μg kg–1, respectively. Asian rice contained mainly inorganic As (iAs; 86–99%), whereas 18–26% of the tAs in Australian-grown rice was dimethylarsinic acid (DMA). Relatively higher concentrations of tAs in Australian-grown rice than that in imported rice of Asian origin suggest that Australian-grown rice may be a health risk for the consumers. It was estimated that Australian-grown organic brown rice can contribute up to 98% of the FAO/WHO recommended maximum tolerable daily intake limit of iAs (2.1 μg kg–1 body wt day–1) for Asian immigrants. However, other Australian consumers including European immigrants are unlikely to be at risk to As from rice diets due to their lower rice consumption rates than that of Asian immigrants. The risk assessment showed that imported rice on sale in Australia was likely to pose a lower health risk to consumers than Australian-grown rice.
In the environment, arsenic (As) exists in a number of chemical species, and arsenite (AsIII) and arsenate (AsV) dominate in freshwater systems. Toxicity of As species to aquatic organisms is ...complicated by their interaction with chemicals in water such as phosphate that can influence the bioavailability and uptake of AsV. In the present study, the toxicities of AsIII, AsV and dimethylarsinic acid (DMA) to three freshwater organisms representing three phylogenetic groups: a phytoplankton (Chlorella sp. strain CE-35), a floating macrophyte (Lemna disperma) and a cladoceran grazer (Ceriodaphnia cf. dubia), were determined using acute and growth inhibition bioassays (EC50) at a range of total phosphate (TP) concentrations in OECD medium. The EC50 values of AsIII, AsV and DMA were 27±10, 1.15±0.04 and 19±3mg L−1 for Chlorella sp. CE-35; 0.57±0.16, 2.3±0.2 and 56±15mgL−1 for L. disperma, and 1.58±0.05, 1.72±0.01 and 5.9±0.1mgL−1 for C. cf. dubia, respectively. The results showed that AsIII was more toxic than AsV to L. disperma; however, AsV was more toxic than AsIII to Chlorella sp. CE-35. The toxicities of AsIII and AsV to C. cf. dubia were statistically similar (p>0.05). DMA was less toxic than iAs species to L. disperma and C. cf. dubia, but more toxic than AsIII to Chlorella sp. CE-35. The toxicity of AsV to Chlorella sp. CE-35 and L. disperma decreased with increasing TP concentrations in the growth medium. Phosphate concentrations did not influence the toxicity of AsIII to either organism. Chlorella sp. CE-35 showed the ability to reduce AsV to AsIII, indicating a substantial influence of phytoplankton on As biogeochemistry in freshwater aquatic systems.
Biotransformation of As species by phytoplankton: (A) Arsenate (AsO43−) competes with phosphate (PO43−) for uptake transporters in the cell membrane. Phytoplankton actively takes up AsO43− under low phosphate condition because they mistake it for PO43−. Arsenate is then reduced to AsIII and subsequently biotransformed to DMA, MMA and complex organoarsenic compounds before excretion into the water. (B) Uptake and biotransformation of AsV by phytoplankton as influenced by phosphate concentrations in the medium. Arrows indicate the PO43− concentrations in the medium (thick and thin arrows are for low and high phosphate concentrations, respectively). Display omitted
•AsIII was more toxic than AsV to L. disperma, while the opposite was for Chlorella sp. CE-35.•AsIII and AsV showed similar toxicity to cladoceran grazer (Ceriodaphnia cf. dubia).•DMA was less toxic than AsIII and AsV to L. disperma and C. cf. dubia, but more toxic than AsIII to Chlorella sp. CE-35.•Phosphate concentrations have significant influence on AsV toxicity to all the three organisms.
Rising temperatures (1.4–6°C) due to climate change have been predicted to increase cyanobacterial bloom occurrences in temperate water bodies; however, the impacts of warming on tropical ...cyanobacterial blooms are unknown. We examined the effects of four different temperatures on the growth rates and microcystin (MC) production of five tropical Microcystis isolates (M. ichthyoblabe (two strains), M. viridis, M. flos-aquae, and M. aeruginosa). The temperature treatments are based on current temperature range in Singapore's reservoirs (27°C and 30°C), as well as projected mean (33°C) and maximum temperatures (36°C) based on tropical climate change estimates of +6°C in air temperature. Increasing temperatures did not significantly affect the maximum growth rates of most Microcystis strains. Higher growth rates were only observed in one M. ichthyoblabe strain at 33°C and M. flos-aquae at 30°C where both were isolated from the same reservoir. MC-RR and MC-LR were produced in varying amounts by all four species of Microcystis. Raised temperatures of 33°C were found to boost total MC cell quota for three Microcystis strains although further increase to 36°C led to a sharp decrease in total MC cell quota for all five Microcystis strains. Increasing temperature also led to higher MC-LR:MC-RR cell quota ratios in M. ichthyoblabe. Our study suggests that higher mean water temperatures resulting from climate change will generally not influence growth rates of Microcystis spp. in Singapore except for increases in M. ichthyoblabe strains. However, toxin cell quota may increase under moderate warming scenarios depending on the species.
The individual and combined effects of copper, cadmium, and zinc on the cell division rate of the tropical freshwater alga Chlorella sp. were determined over 48 to 72 h. Metal mixtures were prepared ...based on multiples of their single‐metal median effective concentration (EC50) values, i.e., toxic units (TU) using a triangular mixture design with five toxicant levels (0, 0.75, 1.0, 1.25, and 1.5 TU). Single‐metal EC50 values after a 72‐h exposure were 0.11, 0.85, and 1.4 μM for copper, cadmium, and zinc, respectively. Significant interactions were observed for all metal combinations after 48 and 72 h. An equitoxic mixture of Cu 1 Cd was more than concentration additive (synergistic) to the growth of Chlorella sp., while combinations of Cu + Zn, Cd + Zn, and Cu + Cd + Zn were all less than concentration additive or were antagonistic. To determine the effect of each metal on the uptake of the other, extracellular (membrane‐bound) and intracellular metal concentrations, both alone and in mixtures, were compared. The increased growth inhibition observed for mixtures of Cu + Cd was due to higher concentrations of cell‐bound and intracellular copper in the presence of cadmium compared with copper alone (i.e., cadmium‐enhanced copper uptake). In contrast, both extra‐ and intracellular cadmium concentrations were reduced in the presence of copper. In mixtures of Cu + Zn, copper also inhibited the binding and cellular uptake of zinc, which resulted in decreased toxicity. Zinc had no appreciable effect on the uptake of copper by Chlorella sp. Our results suggest that all three metals share some common uptake and transport sites on Chlorella cells and that copper out competes both cadmium and zinc for cell binding. Determination of metal cell distribution coefficients (Kd) confirmed that Kd values for cadmium and zinc in single‐metal exposures decreased in the presence of copper.
Algal toxicity tests based on growth inhibition over 72 h have been extensively used to assess the toxicity of contaminants in natural waters. However, these laboratory tests use high cell densities ...compared to those found in aquatic systems in order to obtain a measurable algal response. The high cell densities and test duration can result in changes in chemical speciation, bioavailability, and toxicity of contaminants throughout the test. With the recent application of flow cytometry to ecotoxicology, it is now possible to use lower initial cell densities to minimize chemical speciation changes. The speciation and toxicity of copper in static bioassays with the tropical freshwater alga Chlorella sp. and the temperate species Selenastrum capricornutum (Pseudokirchneriella subcapitata) were investigated at a range of initial cell densities (102‐105 cells/ml). Copper toxicity decreased with increasing initial cell density. Copper concentrations required to inhibit growth (cell division) rate by 50% (72‐h median effective concentration EC50) increased from 4.6 to 16 μg/L for Chlorella sp. and from 6.6 to 17 μg/L for S. capricornutum as the initial cell density increased from 102 to 105 cells/ml. Measurements of anodic stripping voltammetry—labile, extracellular, and intracellular copper confirmed that at higher initial cell densities, less copper was bound to the cells, resulting in less copper uptake and lower toxicity. Chemical measurements indicated that reduced copper toxicity was due primarily to depletion of dissolved copper in solution, with solution speciation changes due to algal exudates and pH playing a minor role. These findings suggest that standard static laboratory bioassays using 104 to 105 algal cells/ml may seriously underestimate metal toxicity in natural waters.
Herbicides are common pollutants of rivers in agricultural regions. These contaminants include various types of chemicals with different modes of toxic action. Herbicides can have toxic effects on ...freshwater benthic diatoms, the base of the aquatic food web. We examined the effects of (non-mixture) herbicide exposure to the health of diatoms for eight common herbicides with three different modes of action; the photosystem II (PSII) inhibitors: atrazine, simazine, hexazinone, tebuthiuron and diuron; two auxinic herbicides: MCPA and 2,4-D; and the EPSP synthase inhibitor: glyphosate. Benthic diatoms within riverine communities were exposed to each herbicide in rapid toxicity tests at concentrations of 50, 200 and 500μgL−1. The most sensitive taxa were Gomphonema spp. and Encyonema gracilis. Navicula cryptotenella was the most tolerant to herbicide exposure. There was no significant effect of the different herbicide modes of action at the community level. Herbicide mode of action did not alter which taxa were most sensitive within the community and sensitivity rankings of the dominant diatom taxa were similar for each of the eight herbicides. The consistency of the results between herbicides suggests that freshwater benthic diatoms may be suitable in situ indicators for detecting the toxicity of herbicides with differing modes of action.
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•We assessed the response of a riverine benthic diatom community to eight herbicides.•The relative sensitivity of the diatom taxa was similar for each of the herbicides.•Herbicide mode of action did not alter which taxa were most sensitive.•There was no effect of herbicide mode of action at the community level.
