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PubMed1987

Fate of 2,5,4'-trichlorobiphenyl in outdoor ponds and its uptake via the food chain compared with direct uptake via the gills in grass carp and rainbow trout.

A field experiment was carried out to investigate the fate and the extent to which food chain transfer of a PCB congener (2,5,4'-trichlorobiphenyl; 3-CB) could affect its potential for bioaccumulation. Three 35-m3 ponds were each stocked with 25 rainbow trout (a carnivore) and 20 grass carp (a herbivore). 3-CB was supplied to each pond at a nominal concentration of 14 micrograms liter-1. Samples of water, sediment, grass carp, rainbow trout, aquatic plants, and invertebrates were removed at intervals from 0 to 28 days after treatment and residues of 3-CB were determined using gas-liquid chromatography with electron-capture detection. The fate of 3-CB in the ponds was determined by transport rather than degradation processes. Evaporation accounted for 86-87% loss and sorption onto sediment and biota for 11-12% loss of 3-CB from the pond water after 28 days. The kinetics of transport between water, air, sediment, and biota were studied after fitting the data to a three-compartment model. This model was used to calculate rates of evaporation (ke) and sorption. The calculated value for ke was in good agreement with predictions based on fundamental relationships between Henry's constant, windspeed, and ke. Residues of 3-CB in rainbow trout accumulated to a significantly greater extent (P less than 0.05) than in grass carp. This difference could not be explained by differences in growth rates, distribution of lipids, or by a difference in rates of metabolism. The most plausible explanation is that there was a difference in accumulation of 3-CB residues via the food chain. This experimental work supports the conclusion, suggested by a modeling approach of other workers, that food chain accumulation of PCBs can be an important route for uptake when environmental concentrations are very low.

Animals↗
PubMed1999

Accumulation of potentially toxic elements in plants and their transfer to human food chain.

Contaminated soils can be a source for crop plants of such elements like As, Cd, Cr, Cu, Ni, Pb, and Zn. The excessive transfer of As, Cu, Ni, and Zn to the food chain is controlled by a "soil-plant barrier"; however, for some elements, including Cd, the soil-plant barrier fails. The level of Cd ingested by average person in USA is about 12 micrograms/day, which is relatively low comparing to Risk Reference Dose (70 micrograms Cd/day) established by USEPA. Food of plant origin is a main source of Cd intake by modern society. Fish and shellfish may be a dominant dietary sources of Hg for some human populations. About half of human Pb intake is through food, of which more than half originates from plants. Dietary intake of Cd and Pb may be increased by application of sludges on cropland with already high levels of these metals. Soils amended with sludges in the USA will be permitted (by USEPA-503 regulations) to accumulate Cr, Cd, Cu, Pb, Hg, Ni, and Se, and Zn to levels from 10 to 100 times the present baseline concentrations. These levels are very permissive by international standards. Because of the limited supply of toxicity data obtained from metals applied in sewage sludge, predictions as to the new regulations will protect crop plants from metal toxicities, and food chain from contamination, are difficult to make.

Agriculture↗
PubMed1998

Food chain dynamics in the chemostat.

The asymptotic behavior of a tri-trophic food chain model in the chemostat is studied. The Monod-Herbert growth model is used for all trophic levels. The analysis is carried out numerically, by finding both local and global bifurcations of equilibria and of limit cycles with respect to two chemostat control parameters: the dilution rate of the chemostat and the concentration of input substrate. It is shown that the bifurcation structure of the food chain model has much in common with the bifurcation structure of a one-dimensional map with two turning points. This map is used to explain how attractors are created and destroyed under variation of the bifurcation parameters. It is shown that low as well as high concentration of input substrate can lead to extinction of the highest trophic level.

Animals↗
PubMed2003

A ratio-dependent food chain model and its applications to biological control.

While biological controls have been successfully and frequently implemented by nature and human, plausible mathematical models are yet to be found to explain the often observed deterministic extinctions of both pest and control agent in such processes. In this paper we study a three trophic level food chain model with ratio-dependent Michaelis-Menten type functional responses. We shall show that this model is rich in boundary dynamics and is capable of generating such extinction dynamics. Two trophic level Michaelis-Menten type ratio-dependent predator-prey system was globally and systematically analyzed in details recently. A distinct and realistic feature of ratio-dependence is its capability of producing the extinction of prey species, and hence the collapse of the system. Another distinctive feature of this model is that its dynamical outcomes may depend on initial populations levels. Theses features, if preserved in a three trophic food chain model, make it appealing for modelling certain biological control processes (where prey is a plant species, middle predator as a pest, and top predator as a biological control agent) where the simultaneous extinctions of pest and control agent is the hallmark of their successes and are usually dependent on the amount of control agent. Our results indicate that this extinction dynamics and sensitivity to initial population levels are not only preserved, but also enriched in the three trophic level food chain model. Specifically, we provide partial answers to questions such as: under what scenarios a potential biological control may be successful, and when it may fail. We also study the questions such as what conditions ensure the coexistence of all the three species in the forms of a stable steady state and limit cycle, respectively. A multiple attractor scenario is found.

Animals↗
PubMed2002

Food chain differences affect heavy metals in bird eggs in Barnegat Bay, New Jersey.

There is an abundance of field data on levels of mercury in a wide variety of birds and on a suite of heavy metals in single species of birds, but few studies examine a suite of metals in a suite of birds that represent different trophic levels. Thus it is often difficult to determine whether food chain differences exist and have ecological relevance for the birds. In this paper I examine the levels of seven metals in the eggs of five species of marine birds that nest in Barnegat Bay, New Jersey to determine whether there are differences among species and whether such differences reflect food chain differences. There were significant differences among species for all metals, except cadmium, with black skimmers (Rynchops niger) having the highest levels of all metals except manganese and selenium. Metal concentrations in eggs mainly represented food chain differences. Mercury exhibited the greatest interspecific difference, with skimmer eggs having five times higher mercury levels than the eggs of great black-backed gulls (Larus marinus). Although there were significant interspecific differences in the other metals, they were generally less than an order of magnitude. There were few high, significant correlations among metals, although mercury was positively correlated with arsenic overall. Mean mercury levels exceeded the level known to adversely affect development in bird eggs for common (Sterna hirundo) and Forster's (Sterna forsterii) terns and for skimmers and exceeded the mean for eggs of fish-eating birds reported from 68 studies.

Animals↗
PubMed1984

State of research: environmental pathways and food chain transfer.

Data on the chemistry of biologically active components of petroleum, synthetic fuel oils, certain metal elements and pesticides provide valuable generic information needed for predicting the long-term fate of buried waste constituents and their likelihood of entering food chains. Components of such complex mixtures partition between solid and solution phases, influencing their mobility, volatility and susceptibility to microbial transformation. Estimating health hazards from indirect exposures to organic chemicals involves an ecosystem's approach to understanding the unique behavior of complex mixtures. Metabolism by microbial organisms fundamentally alters these complex mixtures as they move through food chains. Pathway modeling of organic chemicals must consider the nature and magnitude of food chain transfers to predict biological risk where metabolites may become more toxic than the parent compound. To obtain predictions, major areas are identified where data acquisition is essential to extend our radiological modeling experience to the field of organic chemical contamination.

Air Pollutants↗
PubMed2006

Perchlorate in the United States. Analysis of relative source contributions to the food chain.

Perchlorate has been considered by some a potential threat to human health, especially to developing infants and children because it may inhibit iodide uptake by the sodium iodide symporter (NIS) of the thyroid. In the United States, during the last several decades, environmental perchlorate has had three recognized sources stemming from (a) its use as an oxidizer (including in rocket propellants), (b) its presence in Chilean nitrate fertilizer (CNF), and (c) natural production. An analysis of the relative source strengths and how they may influence entry into the food chain has not been conducted. Averaged over the last --60 years, we estimate that the source strengths have been (a) 10.6, (b) 0.75, and (c) 0.13-0.64 Gg/y for the United States as a whole. Of this, while (b) and (c) represent actual dispersed amounts, the figure in (a) is the amount of perchlorate produced and only a fraction (f) of it has been dispersed and often in a more localized fashion. In addition, dispersal of (b) has taken place only over agricultural land. Considering that the total land area in the United States is 5.5 x the arable land area, in terms of incorporation into the food chain,the figure cited in (b) has a proportionately greater impact. Most estimates of fwill thus suggest that over the considered period, the contribution of CNF to incorporation of perchlorate in the food chain has likely been comparable to oxidizer perchlorate, with natural production being a lesser source. Fireworks presently constitute a potentially important source of increasing importance but a quantitative impact cannotyet be assessed.

Biological Availability↗
PubMed2001

Availability of cadmium and zinc from sewage sludge to the flounder, Platichthys flesus, via a marine food chain.

This paper examines the potential availability to a demersal fish of cadmium and zinc associated with digested sewage sludge, via a food chain as well as directly from the sludge, and the tissue distribution and possible excretion of any accumulated cadmium and zinc. Radioactive tracer techniques were used in order to follow the food chain transfer of the metals. Flounder (Platichthys flesus) accumulated cadmium both directly from sludge (delivered in newly ingested unassimilated gutfuls in the amphipods) and in assimilated form from the tissues of the amphipod crustacean Corophium volutator that had been feeding on a sludge-sediment mixture. Cadmium from both sources could be excreted by the fish. The concentration of cadmium within the whole fish increased as the input of cadmium in the diet increased. Zinc, similarly, is available to the flounder both directly from sludge and from zinc accumulated in C. volutator. Only a limited increase in net accumulation of zinc by the flounder was observed upon increased inputs of zinc through the diet, perhaps indicating some regulation of body zinc concentration by the flounder.

Animals↗
PubMed2001

Food chain chaos due to junction-fold point.

Consideration is given to a basic food chain model satisfying the trophic time diversification hypothesis which translates the model into a singularly perturbed system of three time scales. It is demonstrated that in some realistic system parameter region, the model has a unimodal or logistic-like Poincare return map when the singular parameter for the fastest variable is at the limiting value 0. It is also demonstrated that the unimodal map goes through a sequence of period-doubling bifurcations to chaos. The mechanism for the creation of the unimodal criticality is due to the existence of a junction-fold point [B. Deng, J. Math. Biol. 38, 21-78 (1999)]. The fact that junction-fold points are structurally stable and the limiting structures persist gives us a rigorous but dynamical explanation as to why basic food chain dynamics can be chaotic. (c) 2001 American Institute of Physics.

Journal Article↗
PubMed1997

Experimental evidence for a behavior-mediated trophic cascade in a terrestrial food chain.

Predators of herbivorous animals can affect plant populations by altering herbivore density, behavior, or both. To test whether the indirect effect of predators on plants arises from density or behavioral responses in a herbivore population, we experimentally examined the dynamics of terrestrial food chains comprised of old field plants, leaf-chewing grasshoppers, and spider predators in Northeast Connecticut. To separate the effects of predators on herbivore density from the effects on herbivore behavior, we created two classes of spiders: (i) risk spiders that had their feeding mouth parts glued to render them incapable of killing prey and (ii) predator spiders that remained unmanipulated. We found that the effect of predators on plants resulted from predator-induced changes in herbivore behavior (shifts in activity time and diet selection) rather than from predator-induced changes in grasshopper density. Neither predator nor risk spiders had a significant effect on grasshopper density relative to a control. This demonstrates that the behavioral response of prey to predators can have a strong impact on the dynamics of terrestrial food chains. The results make a compelling case to examine behavioral as well as density effects in theoretical and empirical research on food chain dynamics.

Journal Article↗
PubMed2002

On the dynamics of discrete food chains: low- and high-frequency behavior and optimality of chaos.

In this paper we derive and analyze a discrete version of Rosenzweig's (Am. Nat. 1973) food-chain model. We provide substantial analytical and numerical evidence for the general dynamical patterns of food chains predicted by De Feo and Rinaldi (Am. Nat. 1997) remaining largely unaffected by this discretization. Our theoretical analysis gives rise to a classification of the parameter space into various regions describing distinct governing dynamical behaviors. Predator abundance has a local optimum at the edge of chaos.

Animals↗
PubMed2002

Transfer and effects of cadmium in an experimental food chain involving the snail Helix aspersa and the predatory carabid beetle Chrysocarabus splendens.

The transfer and the toxic effects of Cd were studied in an experimental food chain involving the snail Helix aspersa as prey organism and one of its natural predators, the carabid beetle Chrysocarabus splendens. Juvenile snails were fed plant-based food enriched with 0, 10, 50 and 100 microg g(-1) of Cd, then were offered as prey to beetle larvae from egg hatching to pupation stage. Cd concentrations in snail tissues increased with increasing Cd concentration in food and with duration of exposure. Bioaccumulation factors ranged from 1.87 to 3.39, showing that H. aspersa snails, even in their early life stages, belong to macroconcentrator species for Cd. No significant reduction of snail consumption by beetles was found in exposed groups. Cd concentrations in beetle larvae remained very low (lower than 1 microg g(-1) for all groups), demonstrating a very effective regulation capacity in beetle larvae. However, Cd concentrations in highest exposed groups were higher than those found in control groups. Cd contents in adult beetles were lower than in larvae, showing a loss of Cd during metamorphosis. Despite the low Cd concentrations found in beetles, their exposure to Cd contaminated snails led to 31% of mortality, which occurred only during pupation and for the highest exposure level. No clear sublethal effects were found. These results showed that snails inhabiting heavily polluted areas may represent a risk of secondary poisoning for predatory invertebrates and provided quantitative data on the transfer of Cd between two compartments of a terrestrial food chain.

Animals↗
PubMed2001

Lead and cadmium in eggs of colonially nesting waterbirds of different position in the food chain of Greek wetlands of international importance.

Lead and cadmium concentrations were measured in eggs of collonially nesting waterbirds with different position in the food chains of Greek wetlands of international importance. Differences were found between species in the levels of both lead and cadmium in the Evros and Axios Deltas attributable to their different diets. Nevertheless, the concentration in eggs was unrelated to the position of each species studied in its food chain. There was no significant difference in lead levels among four wetlands sampled for the cormorant and in Cd levels among three wetlands sampled for the Mediterranean gull, probably implying species-specific accumulation patterns. A higher lead pollution of the Axios Delta area was only reflected in the eggs of the Mediterranean gull. The very low concentrations of both metals found in the eggs may either suggest low environmental inputs or lack of sensitivity in using eggs as lead and cadmium biomonitors, thus a more sensitive bioindicator still remains to be found.

Animals↗
PubMed2004

A food chain model to predict the levels of lipophilic organic contaminants in humans.

A fugacity-based, nonsteady state, mechanistic model called ACC-HUMAN was developed to describe bioaccumulation of lipophilic organic pollutants from air, water, and soil to humans. The physical environment was linked via a marine and an agricultural food chain model to a human bioaccumulation model. Contaminant uptake via the primary dietary sources of persistent lipophilic contaminants in industrialized countries was addressed, namely fish, dairy products, and beef. In addition, uptake from air and water was considered, allowing the model also to treat less lipophilic compounds. To evaluate the model, the food chain characteristics were parameterized for southern Sweden and historical scenarios of polychlorinated biphenyl (PCB) concentrations in air, water, and soil in this region were constructed from published data. The resulting model predictions of PCB concentrations in fish, milk, beef, and human tissue agreed well with measured concentrations from Swedish monitoring programs. This suggests that ACC-HUMAN is a useful tool for predicting human exposure to bioaccumulative organic compounds. It can be linked easily to existing multimedia fate and transport models.

Agriculture↗
PubMed1992

Ciguatera toxins in the food chain revealed by stable isotopes.

The stable carbon and nitrogen isotope contents of the meat tissues of 27 identifiable fish found in the gut contents of 70 ciguatoxic and non-ciguatoxic barracuda caught along the southwest coast of Puerto Rico have been analyzed. The isotope ratios of those fish found in the stomach contents of ciguatoxic barracuda were significantly different than ratios determined in those fish found in the stomachs of non-ciguatoxic barracuda. The isotope ratios of the toxic dinoflagellate Ostreopsis lenticularis, a presumed vector of ciguatera in the Caribbean were found to be extremely light, particularly for nitrogen. The lightened nitrogen ratios of the herbivore (Doctorfish) and carnivore (Squirrelfish) fishes found in the stomach contents of ciguatoxic barracuda suggest that the dinoflagellate was in the food chain of these barracuda. Results indicate that the trophic pathway of ciguatoxins through the marine food chain from the presumed primary trophic level (dinoflagellates/bacteria) to ciguatoxic barracuda appears to be different than the pathway to non-toxic barracuda. Stable isotope ratios may be a very useful tool for tracing ciguatoxins in the food chain and the identification of ciguatoxic fish.

Animals↗
PubMed2005

Bacterial extracellular polymeric substance (EPS): a carrier of heavy metals in the marine food-chain.

The ecological implications of metal binding properties of bacterial EPS and its possible role in the bioaccumulation of pollutants in the marine food-chain was investigated using a partially purified and chemically characterized microbial EPS isolated from a species of Marinobacter. Various factors influencing metal sorption by the EPS including the influence of initial metal concentrations, incubation time, pH and sodium chloride concentrations on binding of lead (Pb2+) and copper (Cu2+) were evaluated. The bacterial EPS selectively bound more amount of Cu2+ per mg of EPS than Pb2+. Both copper and lead were sorbed more at near neutral pH than acidic pH. The sorption of Cu2+ increased with increasing copper concentration. The estimated maximum binding ability (MBA) of the EPS was 182 nmol copper and 13 nmol lead mg(-1) EPS. However, the sorption of these metals decreased with the increase in sodium chloride concentration. Furthermore, up to 35% of 14C-labeled Marinobacter was ingested by a benthic polychaete Hediste diversicolor. On an average, 29% of the ingested EPS was absorbed into tissues and 49% of the EPS was respired. It was apparent that the animals used the EPS as a source of energy and nutrition. The labile nature of the bacterial EPS and its ability to bind heavy metals might route the bound metals through the marine food chain, thereby transferring and aiding bioaccumulation of metal pollutants in the higher trophic animals.

Adsorption↗
PubMed1982

Top predator persistence in differential equation models of food chains: the effects of omnivory and external forcing of lower trophic levels.

Persistence criteria are given for the highest trophic level predator in ordinary differential equation models of food chains exhibiting arbitrary omnivory and external supplementation of food source or an intermediate predator. The results are expressed in terms of inequalities involving the bounds on the intrinsic growth and interaction rates. Whether omnivory or external forcing enhances persistence is discussed, particularly for the examples of three-, four-, and five-link Lotka-Volterra food chains.

Animals↗
PubMed1991

Food-chain and dose model, CALDOS, for assessing Canada's Nuclear Fuel Waste Management concept.

The food-chain and dose model, CALculation of DOSe (CALDOS), was developed for assessing Canada's concept for nuclear fuel waste disposal in a vault deep in crystalline rock of the Canadian Shield. The model is very general and based on the Shield as a whole. The critical group is totally self-sufficient and represented by ICRP (1975) Reference Man for dose prediction. CALDOS assumes steady-state conditions and deals with variation and uncertainty through Monte Carlo simulation techniques. Ingrowth of some radioactive daughters is considered during food-chain transfer. A limit is set on root uptake to avoid unrealistic plant concentrations. Integrated ingestion and inhalation rates of man are calculated in a unique way, based on energy needs. Soil ingestion by man and external exposure from building material are unique pathways considered. Tritium, 129I, and 222Rn are treated through special models, and 14C and 129I involve unique geosphere dose limits. All transfer coefficients are lognormally distributed, and the plant/soil concentration ratio is correlated with the soil partition coefficient. Animals' ingestion rates are normally distributed and correlated with each other. Comprehensive sets of internal and external dose conversion factors were calculated for CALDOS. Sample calculations show that dose distributions tend to be strongly right-skewed. Many features of CALDOS are relevant for environmental assessment in general.

Animals↗