The importance of trophic transfer in the bioaccumulation of chemical contaminants in aquatic ecosystems

Do Cd, Cu, Ni, Pb, and Zn biomagnify in aquatic ecosystems?

In this review, we sought to assess from a study of the literature whether five in organic metals (viz., cadmium, copper, lead, nickel, and zinc) bio magnify in aquatic food webs. We also examined whether accumulated metals were toxic to consumers/predators and whether the essential metals (Cu and Zn and possibly Ni) behaved differently from non-essential ones (Cd and Pb). Biomagnification potential was indexed by the magnitude of single and multiple trophic transfers in food chains. In this analysis, we used three lines of evidence-laboratory empirical, biokinetic modeling, and field studies-to make assessments. Trophic transfer factors, calculatedfrom lab studies, field studies, and biokinetic modeling, were generally congruent.Results indicated that Cd, Cu, Pb, and Zn generally do not biomagnify in food chains consisting of primary producers, macro invertebrate consumers, and fish occupying TL 3 and higher. However, bio magnification of Zn (TTFs of 1-2) is possible for circumstances in which dietary Zn concentrations are below those required for metabolism. Cd, Cu, Ni, and Zn may biomagnify in specific marine food chains consisting of bivalves, herbivorous gastropods, and barnacles at TL2 and carnivorous gastropods at TL3. There was an inverse relationship between TTF and exposure concentration for Cd, Cu, Pb, and Zn, a finding that is consistent with previous reviews of bioconcentration factors and bioaccumulation factors for metals. Our analysis also failed to demonstrate a relationship between the magnitude of TTFsand dietary toxicity to consumer organisms. Consequently, we conclude that TTFs for the metals examined are not an inherently useful predictor of potential hazard(i.e., toxic potential) to aquatic organisms. This review identified several uncertainties or data gaps, such as the relatively limited data available for nickel, reliance upon highly structured food chains in laboratory studies compared to the unstructured food webs found in nature, and variability in TTFs between the organisms found in different habitats, and years sampled.

Silver as an antimicrobial: facts and gaps in knowledge

Silver has been used for centuries. Today, silver and silver nanoparticles (AgNPs) are used in a wide range of healthcare, food industry, domiciliary applications, and are commonly found in hard surface materials and textiles. Such an extensive use raises questions about its safety, environmental toxicity and the risks associated with microbial resistance and cross-resistance. If the mechanisms of antimicrobial action of ionic silver (Ag+) have been studied, there is little understanding of AgNPs interactions with microorganisms. There have been excellent reviews on the bacterial resistance mechanisms to silver, but there is a paucity of information on resistance to AgNPs. Silver toxicity and accumulation in the environment has been studied and there is a better understanding of silver concentration and species in different environmental compartments. However, owing to the increased applications of silver and AgNPs, questions remain about the presence and consequences of AgNPs in the environment. This review provides an historical perspective of silver usage, an overview of applications, and combined information of microbial resistance and toxicity. Owing the evidence provided in this review, a call for a better understanding and control of silver usage, and for tighter regulations of silver and AgNPs usage is proposed.

Secondary poisoning risk assessment of terrestrial birds and mammals exposed to nickel

The European Union's Existing Substances regulation (EEC 793/93) was developed to assess the ecological risks posed by chemical substances such as Ni and includes the assessment of secondary poisoning risks. The basic structure of this secondary poisoning risk assessment followed the Technical Guidance Document on Risk Assessment and thus included development of predicted exposure concentrations (PECs) and predicted no-effect concentrations (PNECs). A PEC to PNEC ratio greater than 1.0 is indicative of potential risk. The Technical Guidance Document on Risk Assessment provides a generic framework for assessing secondary poisoning risks and prescribes the following terrestrial food chain: soil → earthworm → worm-eating bird or mammal. This secondary poisoning evaluation was conducted at the regional level, and it was found that the generic approach resulted in widespread estimates of potential risk, even at ambient Ni soil concentrations. Accordingly, a tiered approach was used with increasing levels of refinement, including consideration of bioavailability, consideration of a variable diet, and development of dose-based PNEC values. Based on the refined approach, all PEC to PNEC ratios were less than 1.0, except for a ratio of 1.4 in a scenario focused on a regional clay soil, which was of natural origin. This regional-level secondary poisoning evaluation highlighted key risk assessment components that should be considered in future localized secondary poisoning assessments of Ni and other metals, including ingestion rate to body weight ratios for the test organisms used to derive PNECs versus the representative wildlife species evaluated, the appropriateness of high assessment factors for deriving PNECs for naturally occurring essential elements, representative dietary compositions, relative metal bioavailability between the dietary toxicity study and natural diets, and ground-truthing of the risk predictions versus background concentrations.

Assessment of metals in fish from Lake Macquarie, New South Wales, Australia

The concentrations of the metals cadmium, copper, mercury, lead, silver, selenium and zinc were measured in the muscle and gonad tissues of five species of fish, yellowfin bream (Acanthopagrus australis), silverbiddy (Gerres subfasciatus) and trumpeter whiting (Sillago maculata), southern log finned goby (Favonigobious lateralis), and the halfbridled goby (Arenigobius frenatus) from the contaminated Lake Macquarie NSW and three relatively uncontaminated reference estuaries, Wallis Lake, Port Stephens, and St. Georges Basin NSW. Fish from Lake Macquarie were found to have elevated concentrations of selenium, lead, cadmium, and zinc in one or both of these tissues in these species. Increased concentrations relative to background concentrations were most often observed at Cockle Bay, the site with the highest concentrations of these metals in sediments. The degree to which fish accumulated metals appeared to be related to life history characteristics of the species, with sediment-dwelling fish showing the greatest propensity to accumulate metals.

Zinc

The use of zinc in metal alloys and medicinal lotions dates back before the time of Christ. Currently, most of the commercial production of zinc involves the galvanizing of iron and the manufacture of brass. Some studies support the use of zinc gluconate lozenges to treat the common cold, but there are insufficient data at this time to recommend the routine use of these lozenges. Zinc is an essential co-factor in a variety of cellular processes including DNA synthesis, behavioral responses, reproduction, bone formation, growth, and wound healing. Zinc is a relatively common metal with an average concentration of 50 mg/kg soil and a range of 10-300 mg/kg soil. Meat, seafood, dairy products, nuts, legumes, and whole grains contain relatively high concentrations of zinc. The mobility of zinc in anaerobic environments is poor and therefore severe zinc contamination occurs primarily near points sources of zinc release. The recommended daily allowance for adults is 15 mg zinc. The ingestion of 1-2 g zinc sulfate produces emesis. Zinc compounds can produce irritation and corrosion of the gastrointestinal tract, along with acute renal tubular necrosis and interstitial nephritis. Inhalation of high concentrations of zinc chloride from smoke bombs detonated in closed spaces may cause chemical pneumonitis and adult respiratory distress syndrome. In the occupational setting inhalation of fumes from zinc oxide is the most common cause of metal fume fever (fatigue, chills, fever, myalgias, cough, dyspnea, leukocytosis, thirst, metallic taste, salivation). Zinc compounds are not suspected carcinogens. Treatment of zinc toxicity is supportive. Calcium disodium ethylenediaminetetraacetate (CaNa2EDTA) is the chelator of choice based on case reports that demonstrate normalization of zinc concentrations, but there are few clinical data to confirm the efficacy of this agent.

An assessment of the developmental toxicity of inorganic arsenic

A critical analysis of the literature base regarding the reproductive and developmental toxicity of arsenic compounds, with emphasis on inorganic arsenicals, was conducted. The analysis was stimulated by the great number of papers that have purported to have shown an association between exposure of pregnant laboratory animals to arsenic compounds and the occurrence of offspring with cranial neural tube defects, particularly exencephaly. For the most part, the literature reports of arsenic developmental toxicity in experimental animals are inadequate for human risk assessment purposes. Despite the shortcomings of the experimental database, several conclusions are readily apparent when the animal studies are viewed collectively. First, cranial neural tube defects are induced in rodents only when arsenic exposure has occurred early in gestation (on Days 7 [hamster, mouse], 8 [mouse], or 9 [rat]). Second, arsenic exposures that cause cranial neural tube defects are single doses that are so high as to be lethal (or nearly so) to the pregnant animal. Third, the effective routes of exposure are by injection directly into the venous system or the peritoneal cavity; even massive oral exposures do not cause increases in the incidence of total gross malformations. Fourth, repetition of similar study designs employing exaggerated parenteral doses is the source of the large number of papers reporting neural tube defects associated with prenatal arsenic exposure. Fifth, in five repeated dose studies carried out following EPA Guidelines for assessing developmental toxicity, arsenic was not teratogenic in rats (AsIII, 101 micromol/kg/d, oral gavage; 101 micromol/m3, inhalation), mice (AsV, 338 micromol/kg/d, oral gavage; est. 402 micromol/kg/d, diet), or rabbits (AsV, 21 micromol/kg/d, oral gavage). Data regarding arsenic exposure and adverse outcomes of pregnancy in humans are limited to several ecologic epidemiology studies of drinking water, airborne dusts, and smelter environs. These studies failed to (1) obtain accurate measurements of maternal exposure during the critical period of organogenesis and (2) control for recognized confounders. The lone study that examined maternal arsenic exposure during pregnancy and the presence of neural tube defects in progeny failed to confirm a relationship between the two. It is concluded that under environmentally relevant exposure scenarios (e.g., 100 ppm in soil), inorganic arsenic is unlikely to pose a risk to pregnant women and their offspring.

The genetic effects of environmental lead

This article reviews the effects of lead on genetic systems in the context of lead's various other toxic effects and its abundance and distribution in the environment. Lead is perhaps the longest used and best recognized toxic environmental chemical, yet it continued be used recklessly until only very recently. Lead is thus a lesson in the limitations and strengths of science, human conscience and common sense. Lead has been tested and found to be capable of eliciting a positive response in an extraordinarily wide range of biological and biochemical tests; among them tests for enzyme inhibition, fidelity of DNA synthesis, mutation, chromosome aberrations, cancer and birth defects. It reacts or complexes with many biomolecules and adversely affects the reproductive, nervous, gastrointestinal, immune, renal, cardiovascular, skeletal, muscular and hematopoietic systems as well as developmental processes. It is likely that lead is a selective agent that continues to act on and influence the genetic structure and future evolution of exposed plant and animal populations.

Potential for secondary poisoning and biomagnification in marine organisms

For selected priority pollutants, like organochlorine pesticides, PAHs and PCBs, and mercury and cadmium, the transfer along marine food chains was assessed based on monitoring data. Comparison of the acquired body burden for marine fish and the toxicity thresholds for predating marine birds and mammals provides evidence for the relevance of contaminant uptake with the food and the liability for secondary poisoning. As a consequence, contaminant residues in prey organisms (critical body burden) should be used for marine hazard and risk assessments. Evaluations solely from aquatic exposure concentrations are not adequate to account for potential secondary effects in marine ecosystems.

Modelling non-equilibrium concentrations of microcontaminants in organisms: comparative kinetics as a function of species size and octanol-water partitioning

From our experience, risk assessment for environmental management and research purposes is in need of models that apply to many of the species we want to protect from many of the microcontaminants released. The traditional one-compartment model serves as such a tool during interpretation and extrapolation of information on concentration kinetics. Unfortunately, its non-steady parameters are specific for a combination of a compound and a species. So, one must seriously face the prospect that their values will never be measured for most compounds and species due to experimental, ethical and financial constraints. It was therefore considered worthwhile to relate the main non-steady state parameter, viz. the outflow (elimination, clearance, depuration) rate, to common characteristics of compounds and species. The outflow rate (kout) for persistent organic microcontaminants was correlated to the octanol-water partition ratio of the compound (Kow) and the size of the species (z). The regressions for aquatic invertebrates, fish and warm-blooded animals were kout = (1/(4*10(-3)*Kow + 7*10(-8)) + 5*10(-3))*z-0.36 (n = 53, r2 = 0.45), kout = (1/(4*10(-4)*Kow + 5) + 4*10(-3))*z-0.19 (n = 140, r2 = 0.68) and kout = (1/(3*10(-4)*Kow + 2*10(-5)) + 8*10(-3))* z-0.86 (n = 51, r2 = 0.48) respectively. The correlation was less strong if Kow or z were omitted. In addition to the minimum loss rate for persistent compounds, one may distinguish an excess outflow rate (mainly caused by biotransformation) for less persistent organic microcontaminants. The order of magnitude difference is explored and ways to refine these estimations are discussed briefly. Outflow rates for cadmium and mercury are linked to species size with the same type of function. The internal consistency of the model was verified by calculating inflow rates from calibrated outflow rates and comparing these to independent measurements. Moreover, the constants in the regressions are explained physically and their value is compared with those obtained in ecology for consumption, production and respiration. The exponent that scales these rates to the species size is similar to the regressions for outflow rates obtained here. The model allows estimations for fairly unknown substances or species and it is thought to help refining risk evaluations without extensive experimental or desk studies. As this paper shows that joint application of chemical (Kow) and ecological (z) information yields more accurate estimations, this study contributes to the often advocated integration of both disciplines in ecotoxicology.

Comparison of cadmium, mercury and calcium accumulations by isolated hepatocytes of the small skate (Raja erinacea) and rat

1. Accumulation of calcium, cadmium and mercury by isolated hepatocytes of the small skate (Raja erinacea) and rat was examined at 14 and 37 degrees C, respectively. 2. Metal uptakes by both species were biphasic, with rat cells accumulating more metal than the skate cells. 3. Total accumulation after 30 min was in the order: mercury = cadmium much greater than calcium. 4. In both species calcium and cadmium accumulations were reduced at 4 degrees C, while mercury accumulation was not. 5. Cd accumulation was increased by Cu and Hg in both species. 6. Hg accumulation was inhibited by Cu in both species, and increased by Cd only in the rat cells.

Pesticide residues in freshwater and marine zooplankton: a review

A review of the scientific literature on pesticide residues in freshwater and marine zooplankton indicates that despite the great number of pesticides in current use, only residues of the persistent organochlorine insecticides, many of which have been restricted or removed from general use in North America, have been determined. Much of this information is outdated. In addition, with the exception of the Great Lakes on which limited information is available, reports on residues in freshwater zooplankton are rare. Information on residues of the newer, less persistent but heavily used pesticides is lacking. As an alternative to field sampling and chemical analysis of endemic populations of zooplankton, scientists have modeled the bioaccumulation of pesticides in zooplankton using either laboratory microcosms or mathematical equations. However, the extent and importance of trophic transfer to higher food levels through this intermediary group of organisms is still controversial. In addition, the relationship between accumulation of pesticides and toxicity to zooplankton remains unresolved.

Physico-chemical interactions and bioconcentration of zinc and lead in the industrially polluted Husainsagar Lake, Hyderabad, India

This paper deals with the interactions of different physico-chemical parameters in the water profile, and the bioconcentration of zinc and lead in Husainsagar Lake, India. The concentrations of both the metals are within the permissible limits (Indian Council of Medical Research, New Delhi, India (1975). Manual of Standards of Quality for Drinking Water Supplies. ICMR Special Report, p. 44). The concentration of Zn and Pb in the vertical profile were highest in the bottom stratum of the lake and least in the surface stratum. Their concentrations were two to three thousand-fold more in surficial sediments than in the overlying water column. The concentration of Zn increased with increasing trophic level from nanoplankton to zooplankton, but not to fish, and the concentration of Pb decreased with increasing trophic level: nanoplankton --> phytoplankton --> zooplankton --> fish, illustrating no bioconcentration of metals in the classic sense of the term as has been noted for mercury and chlorinated hydrocarbons (DDT).