The influence of mariculture on mercury distribution in sediments and fish around Hong Kong and adjacent mainland China waters

To study the influence of mariculture on mercury (Hg) speciation and distribution in sediments and cultured fish around Hong Kong and adjacent mainland China waters, sediment samples were collected from six mariculture sites and the corresponding reference sites, 200-300 m away from the mariculture sites. Mariculture activities increased total mercury, organic matter, carbon, nitrogen and sulfur concentrations in the surface sediments underneath mariculture sites, possibly due to the accumulation of unconsumed fish feed and fish excretion. However, methylmercury (MeHg) concentrations and the ratio of MeHg to THg (% MeHg) in sediments underneath mariculture sites were lower than the corresponding reference sites. The % MeHg in sediments was negatively correlated (r = −0.579, p < 0.05) with organic matter (OM) content among all sites, indicating that OM may have inhibited Hg methylation in surface sediments. Three mariculture fish species were collected from each mariculture site, including red snapper (Lutjanus campechanus), orange-spotted grouper (Epinephelus coioides) and snubnose pompano (Trachinotus blochii). The average MeHg concentration in fish muscle was 75 μg kg⁻¹ (wet weight), and the dietary intake of MeHg through fish consumption for Hong Kong residents was 0.37 μg kg⁻¹ week⁻¹, which was lower than the corresponding WHO limits (500 μg kg⁻¹ and 1.6 μg kg⁻¹ week⁻¹).     

Nationwide monitoring of mercury in wild and farmed fish from fresh and coastal waters of Korea

Mercury (Hg) concentrations were monitored in wild and cultured fish collected from fresh and coastal waters in the Korean peninsula from April 2006 to August 2008 nationwide. Total Hg concentrations were reported for 5043 fish samples, including 78 species from 133 locations. Significant interspecies variation was noted in the Hg levels. The average Hg concentration in each fish species ranged from 6.31 μg kg⁻¹ for mullet (Mugil cephalus) to 200 μg kg⁻¹ for mandarin fish (Siniperca scherzeri). Among the species collected, the maximum concentration of Hg, 1720 μg kg⁻¹, was measured in an Amur catfish (Silurus asotus). Only wild freshwater fish exceeded the WHO ingestion standard. Wild freshwater piscivorous fish samples from a large artificial upstream lake contained the highest Hg levels. Hg concentrations were compared between fish groups categorized as wild and farmed fish from freshwater and coastal waters. Although the wild freshwater fish had similar size ranges, their Hg concentrations were higher than those of the other groups. Compared to the feed of farmed marine and freshwater fishes, the prey of wild freshwater fish had a higher Hg concentration, and the total Hg concentrations in freshwater and associated sediment samples were higher than those in coastal water and associated sediment samples. In the freshwater environment, piscivorous fish bioaccumulated two times more Hg than carnivorous and omnivorous fish and four times more than planktivorous fish. The difference in Hg concentrations among trophic groups might have been due to differences in the size of fish, in addition to the variations among different trophic groups. These data will be useful for developing the fish consumption advisory as a management measure to reduce Hg exposure.     

Mercury accumulation in the surface layers of mountain soils: a case study from the Karkonosze Mountains, Poland

The study was aimed to examine total concentrations and pools of Hg in surface layers of soils in the Karkonosze Mountains, dependent on soil properties and site locality. Soil samples were collected from a litter layer and the layers 0-10 cm and 10-20 cm, at 68 sites belonging to the net of a monitoring system, in two separate areas, and in three altitudinal zones: below 900 m, 900-1100 m, and over 1100 m. Air-borne pollution was the major source of mercury in soils. Hg has accumulated mainly in the litter (where its concentrations were the highest), and in the layer 0-10 cm. Hg concentrations in all samples were in the range 0.04-0.97 mg kg⁻¹, with mean values 0.38, 0.28, and 0.14 mg kg⁻¹ for litter and the layers 0-10 cm and 10-20 cm, respectively. The highest Hg concentrations in the litter layer were found in the intermediate altitudinal zone, whereas Hg concentrations in the layer 0-10 cm increased with increasing altitude. Soil quality standard for protected areas (0.50 mg kg⁻¹) was exceeded in a few sites. The pools of Hg accumulated in soils were in the range: 0.8-84.8 mg m⁻², with a mean value of 16.5 mg m⁻², and they correlated strongly with the pools of stored organic matter.     

Spatial trend and pollution assessment of total mercury and methylmercury pollution in the Pearl River Delta soil, South China

Total mercury (THg) and methylmercury (MeHg) were measured in large number of soil samples collected from areas with different types of land use, different depth in the Pearl River Delta (PRD) of South China. THg and MeHg concentrations ranged from 16.7 to 3320 ng g⁻¹ and 0.01 to 1.34 ng g⁻¹, respectively. THg levels are highest in the top 0-20 cm soil layer, and decrease from the surface to bottom layer soil. Spatial variation was observed with different types of land use. Urban parks had the highest concentrations and the other areas tended to decrease in the order of residential areas, industrial areas, vegetable fields, cereal fields, and woodlands. Temporal variation was also noted, and two relatively high THg contamination zones located in the northwestern part of the PRD have significantly expanded over the last two decades. Both THg and MeHg concentrations were correlated significantly with soil organic matter (OM), but not with soil pH. THg pollution status was evaluated using two assessment methods.     

Blood mercury levels among fish consumers residing in areas with high environmental burden

Mercury is a ubiquitous, persistent toxicant found in the environment. In water, mercury bioaccumulates up the food chain and leads to high concentrations in fish. Consumption of contaminated fish is the major source of exposure to mercury in the US. The objective of this study was to enroll persons living in areas selected by the Environmental Protection Agency (EPA) to have high mercury concentrations and who consume at least 6 oz of locally caught fish per week to determine the feasibility of monitoring future trends among a population identified as highly exposed. Blood samples were collected at time of interview and analyzed for mercury. Participants (n = 287) were enrolled from North Carolina, Maryland, and South Dakota. Participants reported eating an average of five servings of fish per week. The overall geometric mean for total mercury was 0.75 μg L⁻¹, with North Carolina having the highest mean level (2.02 μg L⁻¹). Overall, 42% of the study population had levels greater than the US geometric mean 0.83 μg L⁻¹. The number of servings of fish consumed was not found to be associated with blood mercury levels. We were able to identify some persons with elevated mercury concentrations living in areas identified by EPA; however, identifying and monitoring a highly exposed population over time would be challenging.     

Toxic metals in commercial marine fish in Oman with reference to national and international standards

Commercially important fresh (581) and frozen (292) marine fish samples of 10 species were collected from seafood factories and evaluated using AAS and ICP-OES. Metal levels significantly (p < 0.05) varied within and between species. However, there were no significant correlations among metals. There were significant interspecific differences for all metals, and yellowfin tuna had the highest level of cadmium and mercury however, red seabream had maximum numbers above the standards. The metal accumulation significantly varied between bottom feeders of intermediately size locally caught fish. The mean cadmium level ranged from 0.0049 to 0.036 mg kg⁻¹ and 1.37% of the total samples exceeded the EU and FAO standards. Mean lead content varied between 0.029 and 0.196 mg kg⁻¹, few samples crossed the EU (2.63%) and FAO (1.6%) limits. Mean mercury level ranged from 0.015 to 0.101 mg kg⁻¹ and none of the samples exceeded the EU limit. Of the total samples analyzed red seabream (2.06%), yellowfin tuna (1.14%), emperor (0.34%), santer bream (0.22%), king fish (0.11%) and skipjack tuna (0.11%) samples crossed the EU limits. In general, fish from these regions are within the safety levels recommended by various organizations and do not pose a health risk in terms of human diet.     

Dental clinics: a point pollution source, not only of mercury but also of other amalgam constituents

Current literature suggests that amalgam waste from dental clinics is a point-source of mercury pollution in the environment. However, apart from mercury, other amalgam constituents (e.g. Ag, Sn, Cu, and Zn) in dental clinics’ wastewater have not been reported in the literature before. The objective of this study was to evaluate the concentrations of mercury and other metals in the wastewater of some dental clinics and the influent of a wastewater treatment plant in Al-Madinah Al-Munawarah (KSA). Samples were collected over a 2-month period from three dental clinics and analyzed for metals using ICP-MS. The mean concentrations of Hg, Ag, Sn, Cu, and Zn in the samples were 5.3 ± 11.1, 0.49 ± 0.96, 3.0 ± 10.7, 10.0 ± 14.5, and 76.7 ± 106 mg L⁻¹, respectively. Additionally, high concentrations of other metals such as Mg (14.4 ± 15.2 mg L⁻¹), Mn (3.0 ± 4.6 mg L⁻¹), Fe (3.0 ± 4.5 mg L⁻¹), Sr (1.6 ± 2.4 mg L⁻¹), and Ba (6.9 ± 10.3 mg L⁻¹) were also found. These values are much higher than the local permissible limits. Most of the metals of interest were also detected in the influent of the wastewater treatment plant. This renders dental clinics wastewater a hazardous waste which should be properly treated before it is discharged into the environment.     

Mercury in the biotic compartments of Northwest Patagonia lakes, Argentina

We report on total mercury (THg) concentrations in the principal components of food webs of selected Northern Patagonia Andean Range ultraoligotrophic lakes, Argentina. The THg contents were determined using Instrumental Neutron Activation Analysis in muscle and liver of four fish species occupying the higher trophic positions (the introduced Salmo trutta, Oncorhynchus mykiss and Salvelinus fontinalis, and the native Percichthys trucha) accounted for eight lakes belonging to Nahuel Huapi and Los Alerces National Parks. We studied the food web components of both the West and East branches of Lake Moreno, including benthic primary producers such as biofilm, mosses, and macrophytes, three plankton fractions, fish, riparian tree leaves, and benthic invertebrates, namely decapods, molluscs, insect larvae, leeches, oligochaetes, and amphipods.Mercury concentrations in fish muscle varied in a wide range, from less than 0.05 to 4 μg g⁻¹ dry weight (DW), without a distribution pattern among species but showing higher values for P. trucha and S. fontinalis, particularly in Lake Moreno.The THg contents of the food web components of Lake Moreno varied within 4 orders of magnitude, with the lower values ranging from 0.01 to 0.5 μg g⁻¹ DW in tree leaves, some macrophytes, juvenile salmonids or benthic macroinvertebrates, and reaching concentrations over 200 μg g⁻¹ DW in the plankton. Juvenile Galaxias maculatus caught in the pelagic area presented the highest THg contents of all fish sampled, reaching 10 μg g⁻¹ DW, contents that could be associated with the high THg concentrations in plankton since it is their main food source. Although Lake Moreno is a system without local point sources of contamination, situated in a protected area, some benthic organisms presented high THg contents when compared with those from polluted ecosystems.     

Comparative study of the accumulation and detoxification of Cu (essential metal) and Hg (nonessential metal) in the digestive gland and gills of mussels Mytilus galloprovincialis, using analytical and histochemical techniques

The aim of the present study is the comparative examination of accumulation and detoxification of Cu and Hg in digestive gland and gills of mussels Mytilus galloprovincialis, using atomic absorption spectrophotometry and autometallography. Mussels were exposed to 0.08 mg L⁻¹ Cu, 0.08 mg L⁻¹ Hg, as well as to a mixture of 0.08 mg L⁻¹ Hg and 0.08 mg L⁻¹ Cu for 11 d. After the experimental exposure, animals were kept under laboratory conditions for a detoxification period of 7 d. An antagonistic effect of Cu against to Hg accumulation was noted in the digestive gland of mussels after the experimental exposure, as well as after the detoxification period, supporting the protective role of Cu against to Hg toxicity in this tissue. Digestive gland was suggested as a main organ for Hg accumulation and gills as a target position for Cu accumulation. Additionally, lower time was evaluated for Hg detoxification in the digestive gland and gills of mussels, in relation to those addressed for Cu detoxification in the same tissues. The evaluation of black silver deposits (BSD) extent performed in digestive gland and gills was suggested as a less sensitive approach, in relation to atomic absorption spectrophotometry (AAS), to indentify the concentration of heavy metals in tissues of mussels. The toxic effects of Hg, Cu and a mixture of them on lysosomal system of the digestive cells are also discussed.     

Reduced mercury deposition in New Hampshire from 1996 to 2002 due to changes in local sources

Changes in deposition of gaseous divalent mercury (Hg(II)) and particulate mercury (Hg(p)) in New Hampshire due to changes in local sources from 1996 to 2002 were assessed using the Industrial Source Complex Short Term (ISCST3) model (regional and global sources and Hg atmospheric reactions were not considered). Mercury (Hg) emissions in New Hampshire and adjacent areas decreased significantly (from 1540 to 880 kg yr⁻¹) during this period, and the average annual modeled deposition of total Hg also declined from 17 to 7.0 μg m⁻² yr⁻¹ for the same period. In 2002, the maximum amount of Hg deposition was modeled to be in southern New Hampshire, while for 1996 the maximum deposition occurred farther north and east. The ISCST3 was also used to evaluate two future scenarios. The average percent difference in deposition across all cells was 5% for the 50% reduction scenario and 9% for the 90% reduction scenario.     

Polybrominated diphenyl ethers (PBDEs) and mercury in fish from lakes of the Tibetan Plateau

High mountains may act as cold traps for globally transported persistent organic pollutants (POPs) and mercury (Hg). In the present study, 60 fish samples were collected from eight alpine lakes across the Tibetan Plateau. Concentrations of polybrominated diphenyl ethers (PBDEs), total mercury (HgT) and methyl mercury (MeHg) were quantified in the fish muscle tissues to improve the understanding of pollution status and factors regulating the transport and fate of these contaminants on the Plateau. The results showed that lake-averaged ∑₁₄PBDEs concentration was between 0.09 ng g⁻¹ dw and 4.32 ng g⁻¹ dw, which was lower than those reported for European mountains. The total mercury concentration in individual fish ranged from 243 to 2384 ng g⁻¹ dw, and that of MeHg from 131 to 1610 ng g⁻¹ dw, which is much higher than those reported in other mountain fish. The spatial variation of PBDEs and mercury in the Plateau is largely controlled by the specific meteorological patterns.     

Accumulation of mercury and methylmercury by mushrooms and earthworms from forest soils

Accumulation of total and methyl-Hg by mushrooms and earthworms was studied in thirty-four natural forest soils strongly varying in soil physico-chemical characteristics. Tissue Hg concentrations of both receptors did hardly correlate with Hg concentrations in soil. Both total and methyl-Hg concentrations in tissues were species-specific and dependent on the ecological groups of receptor. Methyl-Hg was low accounting for less than 5 and 8% of total Hg in tissues of mushrooms and earthworms, respectively, but with four times higher concentrations in earthworms than mushrooms. Total Hg concentrations in mushrooms averaged 0.96 mg Hg kg⁻¹ dw whereas litter decomposing mushrooms showed highest total Hg and methyl-Hg concentrations. Earthworms contained similar Hg concentrations (1.04 mg Hg kg⁻¹ dw) whereas endogeic earthworms accumulated highest amounts of Hg and methyl-Hg.     

Bioaccumulation and trophic transfer of mercury in a food web from a large, shallow, hypereutrophic lake (Lake Taihu) in China

Purpose

Due to the fast development of industry and the overuse of agrichemicals in past decades, Lake Taihu, an important source of aquatic products for Eastern China, has simultaneously suffered mercury (Hg) contamination and eutrophication. The objectives of this study are to understand Hg transfer in the food web in this eutrophic, shallow lake and to evaluate the exposure risk of Hg through fish consumption.

Methods

Biota samples including macrophytes, sestons, benthic animals, and fish were collected from Lake Taihu in the fall of 2009. The total mercury (THg), methyl mercury (MeHg), ??¹³C and ??¹⁵N in the samples were measured.

Results and discussion

The signature for ??¹⁵N increased with the trophic levels. Along with a diet composed of fish, the significant relationship between the ??¹³C and ??¹⁵N indicated that a pelagic foraging habitat is the dominant pathway for energy transfer in Lake Taihu. The concentrations of THg and MeHg in the organisms varied dramatically by ??3 orders of magnitude from primary producers (macrophytes and sestons) to piscivorous fish. The highest concentrations of both THg (100 ng g^?1) and MeHg (66 ng g^?1), however, were lower than the guideline of 200 ng g^?1 of MeHg for vulnerable populations that is recommended by the World Health Organization (WHO). The daily intake of THg and MeHg of 92 and 56 ng day^?1 kg^?1 body weight, respectively, was generally lower than the tolerable intake of 230 ng day^?1 kg^?1 body weight for children recommended by the Joint FAO/WHO Expert Committee on Food Additives. Significant relationships between the ??¹⁵N and the logarithm of THg and MeHg showed an obvious biomagnification of Hg along the food web. The logarithmic bioaccumulation factor of MeHg in the fish (up to 5.7) from Lake Taihu, however, was relatively low compared to that of other aquatic ecosystems.

Conclusion

Health risk of exposure to Hg by consumption of fish for local residents is relatively low in the Lake Taihu area. Dilution of Hg levels in the phytoplankton induced by eutrophication is a possible factor inhibiting accumulation of MeHg in fish in eutrophic Lake Taihu.     

Comparison of concentrations of mercury in ambient air to its accumulation by leafy vegetables: An important step in terrestrial food chain analysis

A biomonitoring network with leafy vegetables was established near a chlor-alkali plant in order to compare the accumulation of mercury to the atmospheric total gaseous mercury (TGM) concentration. Based on data obtained in the reference area the ‘normal’ mercury concentration in vegetables is between 0.6 and 5.4 μg kg⁻¹ FW. The effect detection limits (EDLs) are between 1.2 and 11.0 μg kg⁻¹ FW and the biological detection limits (BDLs), the lowest [TGM] that can be detected significantly, are between 3 and 4 ng m⁻³. The accumulation rate is lowest for lettuce and high for curly kale that proved to be an excellent accumulator and as such it is very useful for biomonitoring purposes. A comparison made in the 1980s between biomonitoring results with grass and the mercury concentration in leafy vegetables from private gardens nearby proved to be valid when applied to the current biomonitoring results with vegetables.     

Food utilization and growth of cutworm Spodoptera litura Fabricius larvae exposed to nickel,and its effect on reproductive potential

Food utilization and growth of the 5th and 6th instar Spodoptera litura Fabricius larvae, and its effect on reproduction potential was evaluated by feeding larvae diets with different doses of Ni for 3 generations. Dose-dependent relationships between Ni levels and food consumption and growth were variable with different larval developmental period and Ni exposure duration. RCR, AD and RGR of the 6th instar larvae were much more affected by Ni exposure than those of 5th instar larvae, and the effects were strongest in the 3rd generation. It was found that RCR was significantly stimulated after 1 and 20 mg kg⁻¹ Ni exposure, while AD was significantly inhibited after 1, 5, 10 and 40 mg kg⁻¹ Ni exposure. However, lower levels of Ni (?5 mg kg⁻¹) significantly increased and higher levels of Ni (?10 mg kg⁻¹) significantly decreased RGR. In 3 successive generations, 10 mg kg⁻¹ Ni significantly increased the ECI and ECD of the 5th instar larvae, and 5 mg kg⁻¹ Ni significantly increased the ECD of the 6th instar larvae. However, ECD were all significantly inhibited with 20 mg kg⁻¹ Ni exposure. Results also revealed that durations of larvae were shortened at low levels of Ni, but extended at high levels of Ni. Fecundity was inhibited by the highest Ni doses in each generation, while improved by low Ni doses in the 3rd generation. Hatching rates in all treatments were significantly decreased in a Ni dose-dependent manner. Study indicated that effects of Ni on these parameters were predominant with the increasing Ni exposure period.     

Effect of dietary fluoride derived from Antarctic krill (Euphausia superba) meal on growth of yellowtail (Seriola quinqueradiata)

Yellowtail (Seriola quinqueradiata) is the most important cultured marine fish in Japan. Dietary fish meal for yellowtail in aquaculture was replaced with 0.0%, 15.4% and 100.0% Antarctic krill meal (KM0, KM15, and KM100) and with 0.0%, 15.4%, and 100.0% low-fluoride krill meal (LFK0, LFK15 and LFK100). The fish was fed to duplicate fish groups for 92 d (KM trial) or 75 d (LFK trial), and fish growth was monitored.Dietary fluoride (F⁻) concentrations (mg kg⁻¹) were 110, 160, and 580 (KM0, KM15, and KM100, respectively) and 98, 120, and 190 (LFK0, LFK15, and LFK100, respectively). The growth during the experimental period, weight gain, feed intake, specific growth rate, and feed efficiency in fish fed the KM100 diet were markedly lower than the other experimental groups, which showed no marked differences in growth performance.After the experiment, dorsal muscle fluoride concentrations in each group were below the detectable limit (1 mg kg⁻¹), but vertebral bone fluoride concentrations increased with increasing proportion of KM to 655 (KM0), 870 (KM15), and 2150 (KM100) mg kg⁻¹. With increasing LFK in the feed, vertebral bone fluoride concentrations (mg kg⁻¹) increased slightly from 500 (LFK0) to 655 (LFK15), and 695 (LFK100). No histopathological changes were detected in the liver tissue in any experimental group.It has been reported that the fluoride bioavailability was reduced with increasing water hardness, however, the dietary fluoride derived from KM exoskeleton accumulates in vertebral bones of marine fish with growth inhibition, as has already been shown for freshwater fish. Vertebral bone fluoride concentrations in two krill-eating Antarctic marine fish in the wild were 33 000 mg kg⁻¹ (Champsocephalus gunnari) and 15 000 mg kg⁻¹ (Notothenia rossii), but they did not show any adverse effect of growth. Therefore, fish bone fluoride accumulation apparently depends on fish species rather than the salinity of the habitat. Consequently, krill exoskeleton must be removed during the processing of Antarctic krill if indeed these krill are to be used as fish feed. However, LFK can completely replace dietary fish meal without apparent adverse effects.     

An exploratory study of total mercury levels in archaeological caribou hair from northwest Alaska

Over the past ten years, total mercury (THg) levels have been surveyed in Alaskan wildlife and fish as part of the Arctic Monitoring and Assessment (AMAP). Beyond these studies there is little historical data on THg levels in important subsistence species for people in Alaska. A survey of THg in caribou hair from archaeological deposits would provide data to develop temporal trends for this region of the Arctic. Caribou hair from a Western Thule settlement beneath the Alaska native village of Deering (ca. AD 1150) show variability in hair THg values, with a mean level (86 ng/g) which is in the range that is observed in modern Rangifer sp. (caribou and reindeer). Hair from House 1 had a THg mean level of 99.6 ng/g and hair from House 2 had a THg mean of 64.2 ng/g. This is the earliest reported record of mercury in caribou associated with human subsistence activities in the western North American Arctic, and is a first step toward compilation of a needed database through which to measure and evaluate exposure to mercury by people who rely heavily on caribou as a food source. We hypothesize that similarity in mercury values in archaeological samples of caribou and in contemporary samples would give an additional perspective on human exposure to mercury through caribou harvest and consumption today. Since this hypothesis will be more useful if evaluated at a regional rather than global scale, further studies will be needed at different archaeological sites across Alaska to determine the generality of this observation in relation to geographic scale.     

Aqueous photoreduction of oxidized mercury species in presence of selected alkanethiols

Mercury is a global environmental contaminant with severe toxicity impact. The chemical processes resulting in the transformation of oxidized mercury species (Hg²⁺) to elemental mercury (Hg⁰), greatly affects the fate and transport of mercury in the natural environment. We hereby provide the first study on the photochemistry of Hg²⁺ with selected alkanethiols (R-SH) as model compounds to represent thiols and thiol-type binding sites on humic substances in natural waters because of the common sulfhydryl functional group (-SH). Kinetic studies were performed using cold vapor atomic fluorescence spectroscopy (CVAFS), the formation of Hg²⁺-thiol complexes (Hg(SR)₂) were confirmed by UV-visible spectrometry and Atmospheric Pressure Chemical Ionization-Mass Spectrometry (APCI-MS), and the reaction products were analyzed using Electron Impact-Mass Spectrometry (EI-MS) and Solid Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry (SPME/GC-MS). Our results indicated that the photoreduction of Hg²⁺ by selected alkanethiols may be mediated by Hg²⁺-thiol complexes to produce Hg⁰. Under our experimental conditions, the apparent first order rate constants obtained for 1-propanethiol, 1-butanethiol, and 1-pentanethiol were (2.0 ± 0.2) × 10⁻⁷ s⁻¹, (1.4 ± 0.1) × 10⁻⁷ s⁻¹, (8.3 ± 0.5) × 10⁻⁸ s⁻¹, respectively. The effects of ionic strength, dissolved oxygen or chloride ion on reaction rates were found to be minimal under our experimental conditions. The identified products of the reaction between oxidized mercury species with selected alkanethiols (C₃-C₅) were Hg⁰ and disulfides (RS-SR). The potential environmental implications are herein discussed.     

Correlation of foliar MT2b expression with Cd and Zn concentrations in hybrid aspen (Populus tremula × tremuloides) grown in contaminated soil

Metal uptake and its effect on foliar metallothionein 2b (MT2b) mRNA levels were studied in hybrid aspen (Populus tremula × tremuloides) in field conditions. The trees were planted on a site contaminated with several metals, including cadmium (mean 5.1 mg kg⁻¹), chromium (80 mg kg⁻¹), copper (180 mg kg⁻¹), nickel (81 mg kg⁻¹), vanadium (240 mg kg⁻¹) and zinc (520 mg kg⁻¹). Of the ten trace elements analyzed, only Cd and Zn accumulated in the leaves with maximal foliar concentrations of 35 and 2400 mg kg⁻¹ (dry weight), respectively. There was a strong correlation between Cd and Zn concentrations and bioaccumulation factors (concentration in plant/soil) in the leaves, branches and roots, suggesting similar transport mechanisms for these two metals. The levels of MT2b correlated with Cd and Zn concentrations in the leaves, demonstrating that increased MT2b expression is one of the responses of hybrid aspen to chronic metal exposure.     

Estimation of daily intake of potentially toxic elements from urban street dust and the role of oral bioaccessibility testing

The pseudo-total and oral bioaccessible concentration of six potentially toxic elements (PTEs) in urban street dust was investigated. Typical pseudo-total concentrations across the sampling sites ranged from 4.4 to 8.6 mg kg⁻¹ for As, 0.2-3.6 mg kg⁻¹ for Cd, 25-217 mg kg⁻¹ for Cu, 14-46 mg kg⁻¹ for Ni, 70-4261 mg kg⁻¹ for Pb, and, 111-652 mg kg⁻¹ for Zn. This data compared favourably with other urban street dust samples collected and analysed in a variety of cities globally; the exception was the high level of Pb determined in a specific sample in this study. The oral bioaccessibility of PTEs in street dust is also assessed using in vitro gastrointestinal extraction (Unified Bioaccessibility Method, UBM). Based on a worst case scenario the oral bioaccessibility data estimated that Cd and Zn had the highest % bioaccessible fractions (median >45%) while the other PTEs i.e. As, Cu, Ni and Pb had lower % bioaccessible fractions (median <35%). The pseudo-total and bioaccessible concentrations of PTEs in the samples has been compared to estimated tolerable daily intake values based on unintentional soil/dust consumption. Cadmium, Cu and Ni are well within the oral tolerable daily intake rates. With respect to As and Pb, only the latter exceeds the TDI_oral if we model ingestion rate based on atmospheric ‘dustiness’ rather than the US EPA (2008) unintentional soil/dust consumption rate of 100 mg d⁻¹. We consider it unlikely that even a child with pica tendencies would ingest as much as 100 mg soil/dust during a daily visit to the city centre, and in particular to the sites with elevated Pb concentrations observed in this study.