Transfer of cadmium in a phytoplankton-oyster-mouse food chain

The trophic transfer of cadmium (Cd) was studied in a phytoplankton-oyster-mouse food chain. Phytoplankton, grown in a continuous culture chemostat system containing CdCl₂ plus the isotope¹⁰⁹Cd, accumulated 70% of the total supplied cadmium. Oysters filtered out 85 to 95% of the phytoplankton. The rate of oyster Cd accumulation at 15 C increased linearly with seawater Cd concentration according to: y=0.066X – 0.15 (n =12, r=0.96); where X=g Cd/L seawater (between 2 and 22) and y=g Cd/g dry wt oyster/ day. About 59% of the Cd accumulated by the oysters came from the phytoplankton food source and 41% from the cadmium dissolved in the water. Sixty-one percent of the total supplied cadmium was retained in the whole soft body of the osyters. Mice fed 0.4 g of oyster-bound Cd per g of diet, retained 0.83% of the dietary cadmium consumed. Mouse kidney retention for organic oyster-bound cadmium was 0.14%. Extrapolation of these results to human risk assessment indicates that moderate consumption of oysters, which are not highly contaminated with cadmium, poses no significant health risk in terms of elevating kidney cadmium levels.     

Lead uptake and release in an experimental trophic chain

A laboratory continuous-flow system was set up to breed a simple trophic chain (Selenastrum capricornutum, Daphnia magna, Poecilia reticulata) in order to evaluate both the accumulation of lead at various levels and the transfer between these levels. The various organisms were bred in separate, but communicating, vessels. This system enables one to distinguish, at the highest trophic level (fish), between bioaccumulation and biomagnification. The experiments demonstrated that lead accumulates in the trophic chain with a decreasing concentration factor from the lowest to the highest levels. As far as fish are concerned, food is the main factor responsible for lead accumulation. Lead accumulated through the alimentary system is subsequently released more slowly than that absorbed through the gills.     

Accumulation of cadmium in a freshwater food chain experimental model

The study of food chain contamination in nature or in the laboratory requires precise definitions of some terms. A simplified model of a freshwater food chain has been elaborated to try to point out hazards related to the presence of cadmium in the aquatic environment. Three different species belonging to various trophic levels, but to the same aquatic systems were used. The required biological and analytical criteria are described. The time course of the experiment was 34 days starting with a 10-day contamination of the first trophic level (algae). The algae were then separated, washed with fresh medium, and given to the second trophic level (daphnids) to eat for 20 days. The third trophic level (fish) was then introduced for 4 days as a scavenger. The methodology was designed to determine the accumulation of cadmium by daphnids and then fish from the algal source. The results show a high direct bioaccumulation of cadmium in algae. The indirect bioaccumulation of daphnids was of the same order of magnitude, but for fish it was smaller. Nevertheless the cadmium transfer from daphnids to fish was obvious.     

Implications for the human food chain of models of cadmium accumulation in sheep

Critical limits for cadmium in parts of the human food chain are considered to have too small margins of safety and some limits are regularly exceeded. There is concern about the exposure of some sections of the population to cadmium in the human food chain, in particular regarding offal, which is a major source of cadmium to some sectors. The kidney is the first organ of sheep to reach the limit of fitness for human consumption. A model (based on a meta-analysis) predicts that this would occur after a mean of just 130 days of feeding sheep the maximum permitted cadmium concentration in feed (in the European Union) in the organic form. Thus it is not surprising that sheep organs are found routinely to exceed cadmium limits. Since reduction of maximum cadmium levels in sheep feed or of the duration of their exposure are not economically viable measures of control, routine removal of liver and kidney from older sheep from the food chain is recommended as the best option to reduce human dietary cadmium intake from sheep origin.     

Evaluating the trophic transfer of selenium in aquatic ecosystems using caged fish, X-ray absorption spectroscopy and stable isotope analysis

This research evaluated the dominant exposure pathways with regard to the bioaccumulation and trophic transfer of selenium (Se) in caged small-bodied fish inhabiting the receiving waters of a uranium-processing mill in northern Saskatchewan, Canada. A 21-day cage study was conducted using wild naïve lake chub (Couesius plumbeus) collected from a reference lake and caged in a reference and an exposure lake downstream of the mill discharge. Caged fish were fed commercially produced Chironomus spp. diets of 1.5 (basal – commercial food) and 5.5 (lab reared in Se-spiked water) μg Se/g (dry weight) at a feeding ration of 10 percent percent body weight/day. Lake chub fed the Se-spiked diet and caged in the reference lake showed increased whole-body Se concentrations compared to chub fed the basal diet after 21 days. Lake chub caged in the exposure lake from both the elevated Se and basal diet groups had significantly greater whole-body Se concentrations compared to the reference lake, and were not significantly different from each other. The use of stable carbon (C), nitrogen (N), and sulphur (S) isotope analyses indicated that alternate benthic food sources native to the exposure lake were likely consumed in conjunction with the controlled diets. Stable isotope analysis of both wild and caged lake chub indicated that the N and S isotopic signatures decreased with increasing Se exposure, which was reflective of the differences in isotopic signatures of the food sources. Dose-dependent substitution of Se for S in methionine as a consequence of dietary Se exposure was illustrated by a decreasing whole-body S isotope signature and an increasing proportion of selenomethionine-like compounds (as measured by synchrotron-based X-ray absorption spectroscopy) with increasing Se exposure. Speciation results from caged lake chub indicated that Se substituted for S in methionine was the dominant Se species found in caged lake chub exposed to dietary sources of Se.     

Selenium uptake and transfer in an aquatic food chain and its effects on fathead minnow larvae

The transfer of Se (Na₂SeO₄) was followed through a laboratory food chain (wateralgae-rotifer-larval fish) and its effect on larval fathead minnows (Pimephales promelas). Selenium transfer between algae (Chlorella pyrenoidosa) and rotifers (Brachionus calyciflorus) was a function of time and food availability. Selenium concentrations in the rotifers ranged from 46 to 91g Se · g^–1 dry weight after 5 hr of feeding. Selenium concentrations (±SD) in larval fish reached 61.1±1.1 g Se · g^–1 dry weight for 9 day-old larvae and 51.7+1.6 g Se · g^–1 for 17 day-old larvae after 7 and 9 days of feeding with Se-contaminated rotifers, respectively. Final dry weights of larvae fed Se-contaminated rotifers were significantly lower than those of controls, although acute toxicity (mortality) was not demonstrated. The biological halflife of food-derived Se in the larvae was 28 days.Based on a thesis by William N. Bennett submitted in partial fulfillment for the degree of Master of Science in Zoology at the University of Wisconsin-Milwaukee.     

Controlling cadmium in the human food chain: a review and rationale based on health effects

Cadmium can cause acute and chronic illness in humans. The evidence for inclusion of Cd among the elements known to be human carcinogens is insufficient. There is scientifically recognized agreement that renal tubular damage and pulmonary emphysema are the two cardinal pathological lesions associated with excessive Cd exposure. Renal tubular damage is the chronic effect attributed to environmental Cd exposure for the nonoccupationally exposed population. For the nonoccupationally exposed population the primary routes of Cd exposure are through food and tobacco smoke. Most persons are in an approximate Cd balance and tend to accrete Cd until approximately age 50, after which a negative balance ensues. Cadmium is accumulated in the renal cortex and concentrations of between 200 300 300 μg/g wet wt generally result in renal dysfunction, with the 200 μg/g level being the most widely accepted number at which the first signs of β₂-microproteinuria occur. In the United States the current mean level of Cd in the kidney cortex is 20–35 μg/g with about 0.6% of the population exceeding 100 μg/g. The impact of increasing soil Cd on the movement of Cd from soil to plant to animal to human would indicate little reason for concern. In contrast, the movement of Cd from soil to plant to human can be of concern. The degree of risk is dependent upon the amount of the diet which is affected, diet selection of the individual, soil pH at which the crop is produced, and the amount of Cd added to the soil.     

Marine fish food in the United States and methylmercury risk

This paper takes a market-oriented approach to study potential exposure of methylmercury (MeHg) risk to human health from US domestic commercial ocean fish landings (consumption). Information is assembled on MeHg concentration levels of marine species. Landings were examined for 1995–2005. Confined to this seafood source, trends of landings indicating high concentration species (above 0.7 ppm, tilefish, shark, king mackerel and swordfish) were significantly decreased. People bought stable amount of medium MeHg level species (0.3–0.7 ppm, grouper, Spanish mackerel) but less amount of low concentration level species (below 0.3 ppm, catfish, tuna and southern flounder). Based on estimated prices of species and quantities taken it is found that consumers, one crucial link of the entire MeHg risk assessment process, had exhibited awareness of potential MeHg risk in fish and demonstrated in household fish consumption. Information assembled in this paper is insufficient to draw further inference on specific population cohorts more susceptible to potential exposure of MeHg risk. This inquiry may be extended to imported fish in the US for comparison.     

Combined effects of methylmercury,lead, and cadmium on hepatic metallothionein and metal concentrations in the pekin duck

This study was initiated to determine the effects of combined treatments of methylmercuric chloride (MeHg), lead acetate (Pb) and cadmium chloride (Cd) administered orally on metallothionein (MT) and metal levels in the liver of the pekin duck (Anas platyrynchos). Methylmercury and Pb induced a two-fold increase in MT while Cd caused a seven-fold increase over controls. Concurrent administration of MeHg and Pb caused no increase in MT over single treatments. The hepatic MT content of the MeHg + Cd and MeHg + Pb + Cd groups was not different from the Cdalone group. Hepatic lead levels were lowest followed by Hg and Cd. Lead increased Hg levels when given simultaneously with MeHg, and further addition of Cd increased this effect. In groups given Pb, MeHg increased hepatic levels of this element, but when MeHg was also given with Cd, the combination produced a reduction in levels of Pb. Lead or MeHg had no effect on Cd levels. Methylmercury, Pb, and their combination elevated hepatic Cu over controls. All treatments significantly raised hepatic Zn levels above controls. Combinations of Cd with either MeHg or Pb lowered Zn levels below that caused by Cd alone. The simultaneous administration of all three metals did not produce Zn levels which were additive. The liver content of iron was not significantly altered.     

The acute and chronic effects of cadmium on the estuarine mysid,Mysidopsis bahia

Summary Mysids, small shrimp-like Crustacea, proved to be a practical bioassay animal for investigating the effects of cadmium in seawater and may serve this purpose for other pollutants. In the laboratory under flow-through test conditions, the mysid,Mysidopsis bahia, was more sensitive to cadmium than other crustaceans tested. LC50 values were 15.5 g/ within 96 hrs and 11.3 g/ during a 17-day life cycle, whereas LC50's for other selected crustaceans were between 120 and 720 g/. Results of life-cycle bioassays can aid in the establishment of water quality criteria for marine and estuarine organisms.     

RADFOOD--a dynamic model for radioactivity transfer through the human food chain

Radioactive fallout presents a short-term risk due to its direct deposition on agricultural crops, as well as a long-term risk resulting from its deposition on soil and subsequent uptake by crops. A dynamic model, RADFOOD, was developed, based on different existing models. It simulates transport of fallout radionuclides through agricultural food chains to man and evaluates the radiation doses resulting from consumption of contaminated food. Transport was modeled through compartments representing various environmental elements of food products. Internal radiation doses (whole-body weighted doses) following ingestion of contaminated foodstuffs were then estimated. Specific types of crops, soils and diet of man and livestock were considered. A sample calculation was performed in which individual and collective radiation doses, as well as associated health effects, resulting from fallout contamination were evaluated. They were estimated for food consumption beginning at various times after the fallout deposition and for different consumption durations. A sensitivity analysis, performed for the main model parameters, showed that the radiation dose is sensitive, for the short-term period, to changes in initial deposition levels and in the parameters characterizing initial fallout interception and resuspension.     

Effects of nutrient enrichment, depuration substrate, and body size on the trophic transfer of cadmium associated with microalgae to the benthic amphipod Leptocheirus plumulosus

Bioavailability and nutrient effects on the trophic transfer of Cd associated with microalgae to the marine benthic amphipod Leptocheirus plumulosus were investigated. Cadmium assimilation efficiency (AE) of suspension-feeding L. plumulosus significantly varied among three algal species tested (Nitzschia punctata, Thalassiosira weissflogii, and Isochrysis galbana). Depuration substrate greatly influenced Cd AE for L. plumulosus (AE was much higher for nonburrowed amphipods), probably because sediment burrowing allowed L. plumulosus to feed as a surface deposit feeder. The L. plumulosus body size, ranging from 0.5 to 2.0 mm, did not affect Cd AE. Nitrate enrichment from 0 to 180 microM in algal culture significantly increased Cd AE from 9.4 to 18.8% for T. weissflogii, from 10.0 to 27.3% for N. punctata, and from 10.0 to 16.2% for I. galbana; nitrate enrichment from 0 to 60 microM did not influence Cd AE in any algal species tested. Physiological turnover rate constants of Cd in L. plumulosus ranged from 0.016 to 0.025/h for the three species and were independent of nitrate addition. Nitrate enrichment strongly enhanced Cd distribution in algal cytoplasm. Phosphate enrichment (0-7.5 miroM) did not significantly affect Cd AEs in L. plumulosus. Overall, a significant linear relationship was observed between the Cd AE of L. plumulosus and the fraction of Cd available in algal cytoplasm. Our work suggests that eutrophication by nitrate enrichment has the potential to enhance the trophic transfer of Cd from microalgae to suspension-feeding benthic invertebrates.     

Biological and chemical factors of importance in the bioaccumulation and trophic transfer of persistent organochlorine contaminants in Arctic marine food webs

Recent studies of arctic marine food webs have provided detailed insights regarding the biological and chemical factors that influence the bioaccumulation and trophic transfer of persistent organochlorine (OC) contaminants in aquatic systems. The present paper summarizes the recent literature with an emphasis on identifying important ecological factors for explaining variability of OC concentrations among organisms. The Arctic ecosystem has a number of unique attributes, including long food chains, reduced diversity of species, similar food webs across the entire region, and limited influence from pollution point sources. Lipid content, body size, age, gender, reproduction, habitat use, migration, biotransformation, seasonal changes in habitat conditions, feeding ecology, and trophic position have all been demonstrated to influence OC concentrations and bioaccumulation in arctic marine biota. The relative importance of each factor varies among OCs and organisms. Diet or trophic level is the dominant factor influencing OC concentrations and dynamics in seabirds and marine mammals, although biotransformation can significantly influence nonrecalcitrant OCs, such as hexachlorocyclohexane isomers. Dietary accumulation of OCs is also an important route of exposure for arctic fish and zooplankton, and biomagnification of OCs may also occur among these organisms. To date, only limited attempts have been made to model trophic transfer of OCs in the arctic marine food web. Although models developed to assess OC dynamics in aquatic food webs have included some biological variables (e.g., lipid content, feeding rate, diet composition, and growth rate), selection of processes included in these models as well as their mathematical solutions and parameterization all introduce simplification. This reduces biological validity of the models and may be particularly problematic in a highly seasonal environment, such as the Arctic Ocean.     

Direct and trophic contamination of the herbivorous carp Ctenopharyngodon idella by inorganic mercury and methylmercury

A comparative analysis of inorganic mercury (Hg(II)) and methylmercury (MMHg) bioaccumulation by the herbivorous fish Ctenopharyngodon idella, via the direct and "direct+trophic" routes, was investigated experimentally. The direct contamination was based on fairly low exposure conditions (Hg(II), 300 ng small middle dotL(-1); MMHg, 30 ng small middle dotL(-1)), for 15 and 30 days. The trophic uptake was based on ingestion of macrophyte leaves (Elodea densa), previously exposed for 87 days to similar Hg concentrations. Results revealed high capacities of bioaccumulation in fish via the direct route, with accumulation factors of 1000 for Hg(II) and 13,000 for MMHg. Hg concentrations measured after direct+trophic contamination were very much greater than those measured after direct exposure, owing to considerable metal burdens accumulated in plants and to large biomasses ingested. Nevertheless, estimated trophic transfer rates were fairly low: 2% for Hg(II) and 13% for MMHg. MMHg determinations in elodea leaves and fish muscle samples reveal significant methylation and demethylation reactions.     

Bioaccumulation and trophic transfer of some brominated flame retardants in a Lake Winnipeg (Canada) food web

The extent of bioaccumulation and trophic transfer of brominated diphenyl ether (BDE) congeners, hexabromocyclododecane (HBCD) diastereoisomers (alpha, beta, and gamma), decabromodiphenylethane (DBDPE), and bis(2,4,6-tribromophenoxy)ethane (BTBPE) was examined in a Lake Winnipeg (Canada) food web. Six species of fish, zooplankton, mussels, sediment, and water from the south basin of the lake were selected for study. Significant positive correlations were found between concentrations of total (sigma) polybrominated diphenylethers (PBDEs; p < 0.005), sigmaHBCDs (p < 0.0001), BTBPE (p < 0.0001), and lipid content in fish. Strong positive linear relationships also were observed from individual plots of BDE 47, BDE 209, and DBDPE concentrations (lipid wt) and trophic level (based on delta15N), suggesting that these compounds biomagnify in the Lake Winnipeg food web. Biomagnification factors varied for the chemicals studied. Plots of log bioaccumulation factors for mussel and zooplankton versus log octanol-water partition coefficient (Kow) were similar and suggest that neither mussels nor zooplankton are in equilibrium with the water. Fifteen BDE congeners were consistently detected in water (dissolved phase, n = 3), with BDE 47 having the greatest concentration (17 pg/L). The rank order of compounds in water (arithmetic mean +/- standard error) were sigmaPBDEs (49 +/- 12 pg/ L) > alpha-HBCD (11 +/- 2 pg/L) > BTBPE (1.9 +/- 0.6 pg/L). Concentrations of DPDPE, BDE 209, and beta- and -gamma-HBCD isomers were below their respective method detection limits (MDLs) in water. Total PBDE concentrations in sediment (n = 4) were greater than any other brominated flame retardant examined in the present study and ranged from 1,160 to 1,610 ng/g (dry wt), with BDE 209 contributing roughly 50% of the total. The gamma-HBCD isomer was detected at concentrations of 50 +/- 20 pg/g (dry wt) in sediment, whereas BTBPE and DBDPE were consistently below their respective MDLs in sediment.     

Cadmium and the food chain: the effect of dietary cadmium on tissue composition in chicks and laying hens.

The cadmium content of body tissues and eggs was studied in broiler chicks and laying hens fed diets supplemented with 3, 12, and 48 microgram/g of cadmium. The 48 microgram/g level was selected as a slightly toxic level while the lower levels were felt to be representative of the amounts of cadmium which would occur in feedstuffs due to environmental contamination. All levels of cadmium resulted in increased cadmium content of kidney while only 12 and 48 microgram/g resulted in increases in the cadmium content of liver and muscle. As little as 3 microgram/g cadmium consistently increased the cadmium content of liver and muscle but this did not prove to be statistically significant. The transfer of dietary cadmium to the egg was found to be very low. Only the 48 microgram/g level resulted in an increase in cadmium content of the egg. This dietary treatment also resulted in reduced egg production and egg shell thickness.