Sorption and accumulation of cadmium in the sediment of the Tama River

Cadmium contents in the water and the sediment samples collected from the Tama River and several branches were measured. Cadmium (above 0.005mgl⁻¹) was detected in only four of the water samples, while the sediment samples showed cadmium content of 1.0–9.8 μg g⁻¹ dry sediment. Cadmium concentration in the sediments of the main stream was correlated against ignition loss of the samples and it was found that 1 g of ignition loss (organic matter) corresponded to 35 μg of cadmium.The batch adsorption experiment in the laboratory using an aqueous solution of cadmium for 14 sediment samples with a higher concentration of cadmium indicated that the amount adsorbed by the sediment is highly dependent on the ignition loss. The amount adsorbed on unit mass of ignition loss q_IL could be correlated by a Freundlich-type equilibrium relation as where C is the equilibrium concentration in the aqueous phase ranging between 7 × 10⁻³ and 10 mg l⁻¹, while k_IL and n are equilibrium constants.The adsorption rate measurement showed that the intraparticle diffusion coefficient of cadmium in the sediment was about 1.1 × 10⁻⁶ cm²s⁻¹, which is of a reasonable order of magnitude assuming the pore diffusion mechanism inside the particle.The results suggest that suspended solid particles of high organic content in flowing water contribute significantly to the transport of cadmium along the river.     

Role of dissolved and particulate cadmium in the accumulation of cadmium in cultured oysters (Crassostrea gigas)

Pacific oysters (Crassostrea gigas) collected on the coast of British Columbia, Canada have occasionally shown cadmium (Cd) concentrations at or above 2 microg g(-1) (wet weight), which has resulted in the loss of some international markets. This study investigated the source and transfer of Cd to oysters by focusing on the role of dissolved and particulate Cd in seawater. Parameters monitored for 1 year at two oyster farm sites on Vancouver Island included: oyster tissue mass and shell length, Cd in oysters, dissolved Cd, particulate Cd, temperature and salinity. Results show that dissolved Cd was the main source of Cd to the oysters and that Cd was mainly concentrated in the gut tissues. A seasonal trend was observed in Cd in oysters, in which levels were lowest during periods of higher temperatures. Results also indicate that the local oceanographic inputs and sediment diagenesis directly affect dissolved Cd and thereby influence the Cd levels in oysters. Particulate matter was not found to be a source of Cd in oysters, and was actually negatively correlated. This was likely due to the uptake of dissolved Cd by phytoplankton and the effect of phytoplankton on oyster tissue mass.     

Selection and breeding of plant cultivars to minimize cadmium accumulation

Natural variation occurs in the uptake and distribution of essential and nonessential trace elements among crop species and among cultivars within species. Such variation can be responsible for trace element deficiencies and toxicities, which in turn can affect the quality of food. Plant breeding can be an important tool to both increase the concentration of desirable trace elements and reduce that of potentially harmful trace elements such as cadmium (Cd). Selection programs for a low-Cd content of various crops, including durum wheat, sunflower, rice and soybean have been established and low-Cd durum wheat cultivars and sunflower hybrids have been developed. In durum wheat (Triticum turgidum L. var durum), low-Cd concentration is controlled by a single dominant gene. The trait is highly heritable, and incorporation of the low-Cd allele can help to reduce the average grain Cd to levels below proposed international limits. The allele for low-Cd concentration does not appear to affect major economic traits and should not cause problems when incorporated into durum cultivars. The cost of Cd selection in a breeding program is initially large both in terms of Cd determination and reduced progress towards development of other economic traits, but declines as more breeding lines in the program carry the low-Cd trait and are utilized in new crosses. Production of low-Cd crop cultivars can be used as a tool to reduce the risk of movement of Cd into the human diet.     

Zinc, nickel and cadmium in carambolas marketed in Guangzhou and Hong Kong, China: implication for human health

Carambola (Averrhoa carambola L.) is a popular juicy fruit throughout the tropical and subtropical world. This study was designed to quantify the levels of zinc (Zn), nickel (Ni) and cadmium (Cd) in carambolas marketed in southern China, and further to evaluate the potential health risk of human consumption of carambola. Zinc concentrations, ranging from 1.471 to 2.875 mg/kg (on fresh weight basis), were below the maximum permissible concentration for Zn in fruit of China (5 mg/kg). However, Ni concentrations (0.134-0.676 mg/kg) were considerably higher than the related recommendation values. Furthermore, Cd concentrations in 51% of the carambolas purchased from Guangzhou exceeded the maximum permissible concentration for Cd in fruit of China (0.03 mg/kg). Our results implicated that the consumption of 0.385 kg carambola contaminated by Cd per day would cause the tolerable daily intake (TDI) of Cd by the consumer to be exceeded. In addition, the remarkably high Ni concentrations in carambolas should also be of concern. The status of heavy metal contamination of carambola products marketed in the other regions and their implications for human health should be identified urgently by in-depth studies.     

The impact of fine sediment accumulation on the survival of incubating salmon progeny: implications for sediment management

This paper draws on results from a recent research programme on the impact of fine sediment transport through catchments to present a case for the development of new approaches to improving the quality of salmonid spawning and incubation habitats. To aid the development of these programmes, this paper summarises the mechanisms by which fine sediment accumulation influences the availability of oxygen (O2) to incubating salmon embryos. The results of the investigation indicate that incubation success is inhibited by: (i) the impact of fine sediment accumulation on gravel permeability and, subsequently, the rate of passage of oxygenated water through the incubation environment; (ii) reduced intragravel O2 concentrations that occur when O2 consuming material infiltrates spawning and incubation gravels; and (iii) the impact of fine particles (clay) on the exchange of O2 across the egg membrane. It is concluded that current granular measures of spawning and incubation habitat quality do not satisfactorily describe the complexity of factors influencing incubation success. Furthermore, an assessment of the trends in fine sediment infiltration indicates that only a small proportion of the total suspended sediment load infiltrates spawning and incubation gravels. This casts doubt over the ability of current catchment-based land use management strategies to adequately reduce fine sediment inputs.     

Responses of industry within Aberdeen to oil related change: Some implications for urban planners

Remaining oil reserves are predominately located offshore. Development of such resources will be accompanied by the growth of onshore supply centres. Location of such centres will depend on possession of an airport and twenty‐four hour port facilities. Aberdeen has recently experienced and responded to such oil related development. The pattern of impact evidenced there may well contain interesting pointers for other areas, particularly within mature economies which are about to be transformed by oil related industrial activity.     

Accumulation of zinc, cadmium and lead by field populations of Lemanea

A study has been made of the concentrations of zinc, cadmium and lead in populations of the red alga Lemanea growing in fast-flowing rivers in Britain, France. Germany, Ireland and Sardinia (Italy). The sites were selected to provide a wide range of aqueous concentrations of these metals. Many of the sites are influenced by past or present mining activities and Lemanea was found at aqueous concentrations of zinc up to 1.16 mg 1⁻¹. In contrast to previous studies with filamentous green algae, no evidence could be found to support the hypothesis that populations differ genetically in their ability to tolerate these heavy metals. Samples of alga consisted of pooled 2 cm long terminal tips of filaments detached from approx. 1 cm² rock surface. Significant positive correlations were found between the logarithm of the mean concentration of zinc, cadmium and lead in four such samples collected from within 10 m reaches at 59 sites and the logarithm of the concentration of each metal in both unfiltered and filtered water. The enrichment ratios for each metal decreased with increasing aqueous metal concentrations. Although the aqueous concentrations of the three metals were strongly intercorrelated, differences in the ratio of metal concentrations were reflected in the composition of Lemanea filaments. The results suggest that high levels of calcium (and/or magnesium) result in decreased uptake of zinc. Intensive sampling from a single population showed that part of the zinc content of filaments is sensitive to short-term fluctuations in concentrations in the surrounding water. In the particular population studied this was about 20%; a similar percentage could be eluted in the laboratory with EDTA. Transplants of Lemanea were made between reaches with different aqueous concentrations of zinc and in all cases the zinc concentration in filament tips increased or decreased to stabilise at a concentration similar to that in filaments native to the reach. It is suggested that chemical analyses of natural or transplanted populations of Lemanea could provide a valuable aid in monitoring contamination of rivers by zinc, cadmium or lead.     

Effects of chelates on plants and soil microbial community: comparison of EDTA and EDDS for lead phytoextraction

Most studies on chelate-induced phytoextraction have focused on EDTA-mediated Pb phytoextraction. But EDTA and the formed EDTA-Pb complexes have low biodegradability and high solubility in soil, resulting in an elevated risk of adverse environmental effects. EDDS is an easily biodegradable chelating agent that has recently been proposed as an environmentally sound alternative to EDTA. Consequently, a greenhouse experiment, using a completely randomized factorial design with four replications, was carried out to compare the potential of EDTA and EDDS for chelate-induced Pb phytoextraction with Cynara cardunculus, as well as to investigate the toxicity of these two chelates to both cardoon plants and soil microorganisms. The effects of chelate addition on soil microbial communities were studied through the determination of a variety of biological indicators of soil quality such as soil enzyme activities, basal and substrate-induced respiration, potentially mineralizable nitrogen, and community level physiological profiles. EDTA was much more efficient than EDDS for the enhancement of root Pb uptake and root-to-shoot Pb translocation. In a soil polluted with 5000 mg Pb kg(-1), as a result of the addition of 1 g EDTA kg(-1) soil, a value of 1332 mg Pb kg(-1) DW shoot was obtained. EDDS application resulted in a shoot Pb accumulation of only 310 mg kg(-1)DW. Plants treated with EDDS showed lower values of biomass than those treated with EDTA. EDDS proved to be rapidly degraded, and less toxic to the soil microbial community in control non-polluted soils. Pb-polluted EDDS-treated soils showed significantly higher values of basal and substrate-induced respiration than those treated with EDTA. Although EDDS had a lower capacity to enhance Pb phytoextraction than EDTA, it has the advantage of rapid biodegradation.     

Phytoprotective influence of bacteria on growth and cadmium accumulation in the aquatic plant Lemna minor

Certain plants are known to accumulate heavy metals, and can be used in remediation of polluted soil or water. Plant-associated bacteria, especially those that are metal tolerant, may enhance the total amount of metal accumulated by the plant, but this process is still unclear. In this study, we investigated metal enhancement vs. exclusion by plants, and the phytoprotective role plant-associated bacteria might provide to plants exposed to heavy metal. We isolated cadmium-tolerant bacteria from the roots of the aquatic plant Lemna minor grown in heavy metal-polluted waters, and tested these isolates for tolerance to cadmium. The efficiency of plants to accumulate heavy metal from their surrounding environment was then tested by comparing L. minor plants grown with added metal tolerant bacteria to plants grown axenically to determine, whether bacteria associated with these plants increase metal accumulation in the plant.Unexpectedly, cadmium tolerance was not seen in all bacterial isolates that had been exposed to cadmium. Axenic plants accumulated slightly more cadmium than plants inoculated with bacterial isolates. Certain isolates promoted root growth, but overall, addition of bacterial strains did not enhance plant cadmium uptake, and in some cases, inhibited cadmium accumulation by plants. This suggests that bacteria serve a phytoprotective role in their relationship with Lemna minor, preventing toxic cadmium from entering plants.     

Zinc, cadmium and lead in water, sediments and submerged plants of the Derwent Reservoir, Northern England

A partial budget is presented of the zinc, cadmium and lead entering the Derwent Reservoir. The mean levels in the water column upstream of the site of inflow are: Zn, 0.216 mg 1⁻¹ ; Cd, 0.003 mg 1⁻¹; Pb, 0.065 mg 1⁻¹; the levels after passage through the 4.1 km² reservoir fall by: Zn, 70.3%; Cd, 98.3%; Pb, 89.2%. Most of these metals are deposited in sediments, the mean values for which are: Zn, 1035 μg⁻¹; Cd, 13μg⁻¹; Pb, 827μg⁻¹. Lead, a higher percentage of which occurs as particulate material, is deposited more rapidly than zinc; this effect is especially obvious when streaming of colder water along the bottom of the reservoir takes place at the time of floods. Macroscopic plants are only occasional in this reservoir, due perhaps in part to heavy metal toxicity. Of the two most common submerged species, Nitella flexilis probably accumulates almost all of its metal content directly from the water, but the data suggest that sediments are a source of some of the heavy metals accumulated by Glyceria fluitans.     

重金属镉对铜藻生长及其生物活性成分积累的影响

为研究水体重金属污染对经济海藻的生长和品质造成的严重影响,以经济褐藻铜藻Sargassum horneri为研究对象,在温度为15℃的条件下,研究了由Cd Cl2·2.5H2O配制不同浓度(0、0.1、0.5、1.0、5.0 mg/L)的重金属镉胁迫对铜藻生长、光合色素、可溶性糖、可溶性蛋白等生理生化指标,以及对生物活性成分(岩藻黄素、褐藻胶和褐藻多酚)积累的影响。结果表明:对照组藻体的特定生长率(SGR)在15 d内持续升高,0.1、0.5 mg/L Cd处理组的SGR在试验前10 d内逐渐升高,然后保持稳定至第15天,1.0 mg/L处理组的SGR随着培养时间的延长呈波动变化状态,而5.0 mg/L处理组的SGR呈先升高后降低的趋势;藻体的各项生理生化指标随胁迫时间呈不同的变化趋势,但在试验第15天时,各胁迫组藻体的叶绿素a、类胡萝卜素和可溶性蛋白含量均显著低于对照组(P<0.05),而可溶性糖含量则显著高于对照组(P<0.05);铜藻的岩藻黄素和褐藻多酚含量在不同浓度的Cd胁迫下均有极大程度的下降,且Cd胁迫浓度越高,降幅越大,而褐藻胶含量在Cd浓度≤0.5 mg/L胁迫下未有显著变化(P>0.05),在Cd≥1.0mg/L时显著下降(P<0.05)。研究表明,在铜藻产业化开发应用过程中,其养殖海域的重金属污染是需要考虑的重要因素。     

Kinetics of bromadiolone in rodent populations and implications for predators after field control of the water vole, Arvicola terrestris

We document the kinetics of bromadiolone in two rodent populations after a field control of water voles, and their implications for predator exposure. Water voles and common voles were trapped aboveground and underground from 1 to 135 days after bromadiolone treatment in the field. Livers, digestive tracts, and rests of the body were analyzed separately.Our results indicate that 99.6% of the water voles trapped underground and 41% of the common voles trapped aboveground contain bromadiolone residues. Concentrations were maximal between 3.3 and 6.5 days after treatment, according to the tissues examined and the model applied for water voles, and after 1.3 to 3.7 days for common voles. Water voles appeared available almost exclusively for foraging predators. Common voles, found less likely to be poisoned and exhibiting weaker concentrations, were mainly sampled aboveground. The liver, primarily eaten by some predators and scavengers, contains a larger bromadiolone quantity (59% of the total amount found in water voles). The rejection of the digestive tract by those species may lead to a subsequent consumption of voles with higher bromadiolone concentrations (from + 3.8 to + 5.8% of concentration) and provide a moderate risk increase. After 135 days, eight of the ten water voles and one of the two common voles exhibited detectable residues. Additionally, one specimen presented higher concentrations than the others, and similar to those measured in Voles trapped between the first 15-20 days. This may have consequences on predator intoxications several months after treatment.These results integrate individual differences for the two main rodent species present in treated areas. Implications for predator exposure were investigated at the end of the study and suggest that, if the risk of secondary poisoning is maximal during the first 15-20 days when the rodent densities remain high, exposure conditions are maintained for at least 135 days.     

Rice as the most influential source of cadmium intake among general Japanese population

The objective of the present study is to examine whether rice is still a leading source of cadmium (Cd) burden among general populations in Japan. For this purpose, 10 prefectures were selected from all over Japan (including the northern- and southern-most Hokkaido and Okinawa prefecture, respectively). Cadmium levels in urine of never-smoking women (corrected for creatinine; Cd-Ucr) were compared with the rice- and wheat product-based Cd intake, which were estimated from Cd contents in rice and wheat (in the forms of bread, noodle and flour) consumed by residents in the areas, and per-capita daily consumption of rice and wheat. Stepwise multiple regression analysis taking Cd-Ucr as a dependent variable and rice- or wheat product-based Cd intakes as independent variables showed that rice was the most influential and almost exclusive variable with a partial correlation coefficient of 0.770-0.832, explaining 59-69% of total variation in Cd-Ucr. The effects of other sources including wheat were essentially negligible.     

Growth of geologic fractures into large-strain populations: review of nomenclature, subcritical crack growth, and some implications for rock engineering

Several aspects of fracture arrays are reviewed briefly and discussed. The terminology applied to progressive or multi-stage brittle deformation in rock masses is improved by noting fundamental mechanical differences in fracture type and the kinematic coupling between dilatant mixed-mode crack displacements and wing cracks developed at the fracture tips. An array of initially mixed-mode (I–II) cracks will evolve under remote tensile least principal stress and with increasing strain to a dilatant, mode-I crack array oriented approximately perpendicular to the remote tensile stress. This progressive fracture growth thus defeats predictions of fracture-set orientation and displacement based only on a Mohr circle estimate of initial elastic stress (valid in the rock mass only at the earliest stages of fracture nucleation). Slow, subcritical crack growth in rock is associated with distinctive changes in fracture population geometry, as shown by published numerical simulations of fracture–network evolution. An increase in the stress corrosion index promotes joint clustering and significant changes in joint length–frequency that may lead to characteristic differences in the statistics of large-strain fracture populations. These geometric clues can be used to refine estimates of strength and deformability of rock masses and to infer classes of physico-chemical processes acting at the fracture tips during the development of the fracture population.     

Aqueous leaching properties and environmental implications of cadmium, lead and zinc trimercaptotriazine (TMT) compounds

2,4,6-Trimercaptotriazine, trisodium salt nonahydrate (TMT-55) is a commercial product that is widely used to chemically precipitate cadmium, lead, zinc and other heavy metals from wastewaters and contaminated natural waters. When mixed with aqueous solutions of TMT-55, aqueous solutions of either reagent-grade zinc, cadmium, or lead salts precipitate crystalline "Zn-TMT", amorphous or crystalline "Cd-TMT" or amorphous "Pb-TMT" (M3[S3C3N3]2.nH2O, where M=Cd2+, Pb2+, and Zn2+ and n> or = 0) that may eventually crystallize if stored in air. Laboratory aqueous leaching studies over 78-106 days using pH 3 HCl, distilled water (pH 6) and pH 9-10 NaOH evaluated the stability of the Cd-, Pb-, and Zn-TMT precipitates. Under pH 3 conditions, the amorphous Cd- and Pb-TMT compounds converted to their crystalline forms and amorphous Cd-TMT also crystallized in distilled water. Otherwise, no decomposition products were detected in the leached solid residues. When compared with the aqueous solubilities of corresponding sulfides and most hydroxides, the TMT compounds were significantly more soluble in distilled water and pH 3 HCl.     

The Nile monitor (Varanus niloticus; Squamata: Varanidae) as a sentinel species for lead and cadmium contamination in sub-Saharan wetlands

Wetland pollution is a matter of concern in sub-Saharan Africa. Though regularly exploited, the Nile monitor (Varanus niloticus), a large amphibious lizard, is not threatened. This work aims at assessing the value of this varanid as a sentinel species in surveys of environmental contamination by metals. Lead and cadmium quantifications were performed by graphite furnace-atomic absorption spectrophotometry in bone, intestine, kidney, liver and muscle in 71 monitors from three unevenly polluted sites in Mali and Niger, plus a reference site. The effects of sex, size and fat reserves as well as factors related to the sampling strategy (tissue sampled, sampling site) were studied with a mixed linear model. Metal contamination is moderate at the four sites but clear differences nevertheless occur. Lead levels are generally maximal in bone, with a gender-independent median value 320 ng.g⁻¹. Median cadmium concentrations never exceed 70.2 ng.g⁻¹ in females (kidney) and 57.5 ng.g⁻¹ in males (intestine). Such levels should have no detrimental effects on the monitors. Lead and cadmium levels in muscles are generally below 200 and 20 ng.g⁻¹, respectively, and should provoke no health hazard to occasional consumers of monitor meat. Metal organotropisms are consistent with those observed in other studies about Squamates: for lead: bone > [kidney, intestine, liver] > muscle in males and [bone, kidney] > [intestine, liver] > muscle in females; for cadmium: [liver, intestine, kidney] > [bone, muscle] for both genders. Females are more contaminated, especially in their kidneys. In this tissue, median values in ng.g⁻¹ are 129.7 and 344.0 for lead and 43.0 and 70.2 for cadmium, for males and females, respectively. Nile monitors can reveal subtle differences in local pollution by metals; moreover, the spatial resolution of the pollution indication that they give seems to be very sharp. The practical relevance of this new tool is thus validated.