Effects of aqueous, dietary and combined exposures of cadmium to Ceriodaphnia dubia

While effects of water-borne metal exposures on freshwater animals have been well documented, the effect of dietary metal exposure is less understood but is gaining importance. However, little attention has been given to the importance of combining both exposure pathways. In this study, we compared effects of aqueous ('water only'), dietary ('food only') and combined ('water+food') exposures of cadmium to the freshwater cladocerans, Ceriodaphnia dubia. Major test endpoints included survival, feeding rate and reproduction. The C. dubia three-brood reproduction tests were conducted according to the United States Environmental Protection Agency (U.S. EPA) methods. Three exposure scenarios were used: aqueous, dietary, and combined aqueous and dietary exposures. Results showed that all three exposures affected survival, feeding rate and reproduction of C. dubia. Interestingly, combined exposure showed contribution effects of aqueous and dietary exposures. Lower cadmium concentrations were needed in combined exposure to produce effects as compared to higher concentrations in aqueous or dietary exposure alone. These results demonstrated the potential importance of dietary and combined exposures for consideration of cadmium regulation and risk assessment of metals.     

Assessment and management of risks arising from exposure to cadmium in fertilisers. I

A risk assessment protocol has been developed for use by individual EU Member States with appropriate selection of input data, to assess the risks to humans and the environment arising from exposure to cadmium in fertilisers. The protocol comprises of three modules: (1) the accumulation module, in which the net accumulation of cadmium in soil and soil solution, resulting from the application of fertiliser, is computed over time. The accumulation module allows for a range of inputs from different sources (atmospheric deposition, sludge addition, manure and fertiliser application) as well as for average and extreme rates of fertiliser application. A critical parameter is the solid/liquid partition coefficient, which in turn is a function of soil properties such as pH and is highly variable depending on the algorithm selected as being representative of national conditions. (2) The exposure module, in which the uptake of cadmium from soil into plants and the subsequent intake of cadmium by humans is computed, using exposure parameters characterising both average and extreme exposure scenarios. The protocol focuses on food types known to be sensitive to cadmium uptake (grain, cereals, potatoes, root vegetables and leafy vegetables). Environmental exposure is also characterised. (3) The risk characterisation module, in which Member States may estimate the incidence and severity of the adverse effects likely to occur due to actual or predicted exposure to cadmium. This is undertaken by modelling the Predicted Environmental Concentrations (PECs) in humans and the environment using the accumulation and exposure modules, and then comparing these values against the relevant Predicted No Effect Concentrations (PNECs). A range of environmental PNEC values are reported in the literature; the European Commission recommends that normally the lowest No Observed Adverse Effect Level (NOAEL) should be used in the risk characterisation. For humans, the current WHO Provisional Tolerable Weekly Intake (PTWI) is equivalent to a daily intake of 70 microg Cd day(-1). Particular risk groups can be characterised, namely of: children; smokers; women with low iron stores; consumers of food items with high cadmium content; and extreme consumers of staple food items. At present, with the data available, it is not possible to characterise risk groups in detail, either at EU level or at Member State level. However, most Member States appear to have an average intake of cadmium which is lower than the WHO's PTWI.     

A system dynamic model for the assessment of different exposure routes in aquatic ecosystems

With the exception of a limited number of highly persistent lipophilic pollutants, waterborne exposure is considered the most relevant exposure route for aquatic organisms, and even the only relevant exposure route in lower tier assessment, while the potential for bioaccumulation is only evaluated as secondary poisoning for birds and mammals. In addition, some evaluations consider that only the dissolved fraction is bioavailable for pelagic organisms. The lack of easy and cost-effective assessment methods is probably the main reason to disregard the contribution of other routes. This paper presents a system dynamics model that estimates the time-dependent accumulation of toxic chemicals through the food chain, and has also the potential to include the exposure from sediment. The generic ecosystem includes a primary producer and three levels of consumers, represented by unicellular algae, cladoceran invertebrates, cladoceran-eating fish and fish-eating fish, respectively. Nevertheless, the model, built using Microsoft Excel software, allows any number of levels and ecological-exposure relationships. The results obtained for four illustrative pollutants demonstrate that factors such as the binding to algae and other edible particles or food chain exposure for lipophilic non-persistent chemicals may constitute significant exposure routes. The current low tier European ecological risk assessment guidelines do not cover these aspects, and therefore may under estimate the real risk for both aquatic organisms and their predators. The model includes a simplified worst-case alternative that normally can be calculated using the existing information. Under a tiered approach, the simplified alternative is proposed to trigger the need of the toxicokinetics assays required to perform the complete time-dependent calculation.     

Bioavailability as an issue in risk assessment and management of food cadmium: a review

The bioavailability of cadmium (Cd) from food is an important determinant of the potential risk of this toxic element. This review summarizes the effects of marginal deficiencies of the essential nutrients zinc (Zn), iron (Fe), and calcium (Ca) on the enhancement of absorption and organ accumulation and retention of dietary Cd in laboratory animals. These marginal deficiencies enhanced Cd absorption as much as ten-fold from diets containing low Cd concentrations similar to that consumed by some human populations, indicating that people who are nutritionally marginal with respect to Zn, Fe, and Ca are at higher risk of Cd disease than those who are nutritionally adequate. Results from these studies also suggest that the bioavailability of Cd is different for different food sources. This has implications for the design of food safety rules for Cd in that if the dietary source plays such a significant role in the risk of Cd, then different foods would require different Cd limits. Lastly, the importance of food-level exposures of Cd and other potentially toxic elements in the study of risk assessment are emphasized. Most foods contain low concentrations of Cd that are poorly absorbed, and it is neither relevant nor practical to use toxic doses of Cd in experimental diets to study food Cd risks. A more comprehensive understanding of the biochemistry involved in the bioavailability of Cd from foods would help resolve food safety questions and provide the support for a badly needed advance in international policies regarding Cd in crops and foods.     

Metal levels in feathers of 12 species of seabirds from midway atoll in the northern Pacific Ocean

Seabirds are excellent subjects for examination of heavy metals because they are long-lived, feed at different distances from land, and exhibit different trophic levels. In this paper we compare the levels of lead, cadmium, mercury arsenic, chromium, manganese, selenium, and tin in the feathers of birds nesting on Midway Atoll in the northern Pacific Ocean. We test the null hypothesis that there are no interspecific differences in the levels of metals in the feathers of the adult black-footed albatross (Diomedea nigripes), Laysan albatross (Diomedea immutabilis), red-footed booby (Sula sula), great frigatebird (Fregata minor), Bonin petrel (Pterodroma hypoleuca), Christmas shearwater (Puffinus nativitatis), red-tailed tropicbird (Phaethon rubricauda), wedge-tailed shearwater (Puffinus pacificus), brown noddy (Anous stolidus), sooty tern (Stema fuscata), grey-backed tern (Stema lunata), and white tern (Gygis alba), and young of some of these species. There were interspecific differences in the levels of all metals for adults. Christmas shearwater had the highest levels of lead, cadmium, selenium and manganese, but the second lowest levels of mercury. In general, metal levels were the lowest in the smallest species (white tern), but were not the highest in the largest species (black-footed albatross), except for manganese, arsenic and mercury. There was a high variance in metal levels among adults for some species, but not for others. White tern adults were variable for lead, while Christmas shearwaters were variable for lead and cadmium. Compared to the means for metals in other birds generally (after Burger, 1993), Christmas shearwaters had higher levels of lead, white terns, brown noddy, Christmas shearwater, frigatebirds and Laysan albatrosses had higher levels of cadmium, and bonin petrel, wedge-tailed shearwater, tropicbirds, frigatebirds, red-footed boobies, and both albatrosses had higher levels of mercury. Whereas the means for lead and cadmium were below the known effects levels, some individuals had levels high enough to cause adverse effects in the birds. The mean values for mercury in Bonin petrel, red-tailed tropicbird, and black-footed albatross were higher than the levels known to cause adverse reproductive and behavioral effects.     

Lead toxicity to wildlife: Derivation of a critical blood concentration for wildlife monitoring based on literature data

Generic risk assessments of lead (Pb) toxicity to wildlife puts soil Pb limits below the natural background. The Tissue Residue Approach (TRA) is an alternative method by which the current risk of Pb to wildlife can be assessed and avoids uncertainties about Pb exposure routes or bioavailability of environmental Pb. About 80 toxicity studies were reviewed of which 19 experimental and 6 field studies with mammals and birds were selected. Blood lead concentration (Pb-B, µg Pb/dL) was used as the index of exposure. The highest No Observed Effect Concentrations (NOECs) varied about 1600-fold among species and tests when expressed as external doses (mg Pb/kg body weight/day) whereas this range reduced to 50-fold when expressed as Pb-B. This illustrates that variation in Pb absorption from diet largely contributes to the variation in critical doses. A critical Pb-B concentration protecting mammals and birds from Pb toxicity was calculated with the HC₅ approach, i.e. the 5th percentile of species NOEC values with data of 15 different species and using growth, reproduction or hematology as endpoints. The HC₅ was significantly lower for mammals than that for birds (p < 0.05), suggesting that the association between blood lead concentration and systemic toxicity was different between the two groups. The HC₅ was 18 µg/dL for mammals and was 71 µg/dL for birds. The dose-response relationship between hematological effects (hemoglobin concentration, hematocrit) and Pb-B was aggregated for different species. These relationships were highly significant and significantly different between mammals and birds. The relationships predict that the % inhibitions of hematological endpoints at the calculated HC₅ values are only 1.5% in mammals and 2% in birds, clearly within the natural variation.     

Eco-SpaCE: An object-oriented, spatially explicit model to assess the risk of multiple environmental stressors on terrestrial vertebrate populations

Wildlife organisms are exposed to a combination of chemical, biological and physical stressors. Information about the relative impact of each stressor can support management decisions, e.g., by the allocation of resources to counteract those stressors that cause most harm. The present paper introduces Eco-SpaCE; a novel receptor-oriented cumulative exposure model for wildlife species that includes relevant ecological processes such as spatial habitat variation, food web relations, predation, and life history. A case study is presented in which the predicted mortality due to cadmium contamination is compared with the predicted mortality due to flooding, starvation, and predation for three small mammal species (Wood mouse, Common vole, and European mole) and a predator (Little owl) living in a lowland floodplain along the river Rhine in The Netherlands. Results indicated that cadmium is the principal stressor for European mole and Little owl populations. Wood mouse and Common vole population densities were mainly influenced by flooding and food availability. Their estimated population sizes were consistent with numbers reported in literature. Predictions for cadmium accumulation and flooding stress were in agreement with field data. The large uncertainty around cadmium toxicity for wildlife leads to the conclusion that more species-specific ecotoxicological data is required for more realistic risk assessments. The predictions for starvation were subject to the limited quantitative information on biomass obtainable as food for vertebrates. It is concluded that the modelling approach employed in Eco-SpaCE, combining ecology with ecotoxicology, provides a viable option to explore the relative contribution of contamination to the overall stress in an ecosystem. This can help environmental managers to prioritize management options, and to reduce local risks.     

Chronic toxicity of the Sava River (SE Europe) sediments and river water to the algae Pseudokirchneriella subcapitata

The Sava River, the largest and most commercially valuable water body in the riparian countries, receives inputs of organic and inorganic compounds from a variety of domestic and industrial activities that may affect the health of human beings and wildlife. In this work, the chronic toxicity of sediment, sediment porewater and surface water from the Sava River and connecting tributaries to the freshwater algae Pseudokirchneriella subcapitata was assessed to characterise the potential impact on aquatic organisms. Samples of different environmental matrices were either tested directly (porewater) or subjected to pre-concentration (sediments and surface water) prior to testing in a 72 h growth inhibition assay using P. subcapitata. The results show that a combination of pre-concentration and bioassay testing was able to characterise the toxic potential and to identify several compartment-specific "hot spots" along the Sava River. Based on the resulting data, a crude risk assessment identified that some of the locations may represent a risk to algae. Additional testing using multiple species and exposure phases is required to conduct a thorough risk assessment, however.     

Ecological food web analysis for chemical risk assessment

Food web analysis can be a critical component of ecological risk assessment, yet it has received relatively little attention among risk assessors. Food web data are currently used in modeling bioaccumulation of toxic chemicals and, to a limited extent, in the determination of the ecological significance of risks. Achieving more realism in ecological risk assessments requires new analysis tools and models that incorporate accurate information on key receptors in a food web paradigm. Application of food web analysis in risk assessments demands consideration of: 1) different kinds of food webs; 2) definition of trophic guilds; 3) variation in food webs with habitat, space, and time; and 4) issues for basic sampling design and collection of dietary data. The different kinds of food webs include connectance webs, materials flow webs, and functional (or interaction) webs. These three kinds of webs play different roles throughout various phases of an ecological risk assessment, but risk assessors have failed to distinguish among web types. When modeling food webs, choices must be made regarding the level of complexity for the web, assignment of species to trophic guilds, selection of representative species for guilds, use of average diets, the characterization of variation among individuals or guild members within a web, and the spatial and temporal scales/dynamics of webs. Integrating exposure and effects data in ecological models for risk assessment of toxic chemicals relies on coupling food web analysis with bioaccumulation models (e.g., Gobas-type models for fish and their food webs), wildlife exposure models, dose-response models, and population dynamics models.     

Mercury, arsenic, cadmium, chromium lead, and selenium in feathers of pigeon guillemots (Cepphus columba) from Prince William Sound and the Aleutian Islands of Alaska

Arsenic, cadmium, chromium, lead, manganese, mercury and selenium were analyzed in the feathers of pigeon guillemots (Cepphus columba) from breeding colonies in Prince William Sound and in the Aleutian Islands (Amchitka, Kiska) to test the null hypothesis that there were no differences in metal levels as a function of location, gender, or whether the birds were from oiled or unoiled areas in Prince William Sound. Birds from locations with oil from the Exxon Valdez Oil Spill in the environment had higher levels of cadmium and lead than those from unoiled places in Prince William Sound, but otherwise there were no differences in metal levels in feathers. The feathers of pigeon guillemots from Prince William Sound had significantly higher levels of cadmium and manganese, but significantly lower levels of mercury than those from Amchitka or Kiska in the Aleutians. Amchitka had the lowest levels of chromium, and Kiska had the highest levels of selenium. There were few gender-related differences, although females had higher levels of mercury and selenium in their feathers than did males. The levels of most metals are below the known effects levels, except for mercury and selenium, which are high enough to potentially pose a risk to pigeon guillemots and to their predators.