Distribution of metallic compounds between plants and soils∗

Distribution of metallic constituents between soil and aerial parts of wild plants has been discussed by using relative ionic impulsions, i/I, defined as functions of concentrations of metallics ions, being i = [M]^1/2M, z_M the oxidation state of considered metal and I = S i the summation of contribution of metals. For this calculation metals were divided into two groups leading to ^I macro (K, Na, Ca, Mg, and Mn, elements accumulated in aerial parts) and to I _Micro (Fe, Cu, Zn, Co and contaminants accumulated in roots). Relative ionic impulsions may be attributed to an electric potential gradient and show if an active or passive uptake is happening. For macroelements linear relationships were obtained for Mg‐K (global active uptake) and Na‐Mn‐Ca (global passive uptake) with inverse slopes. Passive ions seem to be used as counter ions for helping active assimilation. Calculated potential gradient was close to 20 mV. The same situation was found for microelements and pollutants, where Fe is taken passively helping assimilation of the rest (Cu, Zn, Co, Cd, Pb, Ni and Cr) with a potential gradient close to 13 mV. Influences of other ecological segments (rainfall, dry deposition, airborne dust and irrigation), as well as additions for amending contaminated soils are finally discussed.     

Bioconcentration of Cd and Ni in various tissues of two marine bivalves living in different habitats and exposed to heavily polluted seawater

Two marine bivalves, Mytilus galloprovincialis and Callista chione, were exposed to various concentrations of cadmium and nickel (0.5, 1.0, 2.5 and 20 ppm), for 20 days, plus 10 days’ depuration period, in a laboratory experiment. Animals from each experimental condition were dissected and the bioaccumulation and distribution of Cd and Ni were determined in their gills, mantles and remaining bodies. The concentrations of Fe and Zn were also measured. Heavy metal tolerance, bioconcentration and distribution of heavy metals in tissues were considerably different in M. galloprovincialis and C. chione: (i) both animals were tolerant to Ni pollution, even at the highest concentration used; (ii) C. chione was more tolerant to Cd; (iii) M. galloprovincialis was a better Cd and Ni accumulator, with the exception of the highest Cd concentration tested, where C. chione accumulated more Cd; (iv) Fe and Zn levels were much more affected in M. galloprovincialis; (v) in general, accumulation and distribution of Ni and Cd in the tissues were metal-, species- and time of exposure- dependent; (vi) significant amounts of heavy metals remained in the tissues after 10 days’ depuration. Our results support a hypothesis for a two competing processes mechanism for metal accumulation and detoxification.     

The prevalence of heavy metals in Cladophora glomerata L. from Farahabad Region of Caspian Sea – Iran

The presence of toxic heavy metals in the environment is considered as a risk factor for adverse human and environmental health effects. Farahabad Region is a tourist center in the southern coast of Caspian Sea in Mazandaran Province of Iran. Environmental monitoring of this site is important for public health for individuals visiting and residing in this region. Although numerous biomonitoring data are available globally, very few if any apparent investigations have been conducted in this region. In this study, concentration of three heavy metals chromium (Cr), lead (Pb), and cadmium (Cd) was determined for one year in Cladophora glomerata, the predominant macroalga species present in this region. Detection of heavy metals was performed with atomic absorption spectrophotometer using standard methods. Results showed that the range of Cr metal in various algal samples was 29–55 ppm/g dry weight. The levels of Pb in algal samples (Cladophora) ranged from 2 to 8 ppm/g dry weight. The Cd concentrations in C. glomerata biomass ranged from 1.5 to 8.2 ppm/g dry biomass. In view of potential threats of such high metal concentrations in coastal waters and in algal tissues, it is necessary to adopt conservation measures to ensure public health safety.     

Assimilation of trace elements by the mussel Mytilus edulis: effects of diatom chemical composition

Mussels have been widely used as bioindicators of coastal contamination, and recent reports have demonstrated that metals are accumulated from both the dissolved phase and from ingested food. In the winter and spring of 1995, we examined the influence of the chemical composition of food (protein content, trace element concentrations and ratios in the diatom Thalassiosira pseudomana) on the assimilation of six trace elements (Ag, Am, Cd, Co, Se and Zn) in the mussel Mytilus edulis (L.). Differences of up to 38% in diatom protein content had no major influence on the assimilation of any trace element or carbon. Protein assimilation in M. edulis examined with a ³⁵S radiotracer was also independent of protein content in the diatoms. Similarly, Se assimilation in mussels was not affected by the different Se concentrations in the diatoms. Cd assimilation increased with increasing Cd concentration, presumably due to higher desorption of Cd under acidic conditions typical of the mussel gut. Zn assimilation was inversely related to Zn concentration in the food particles, implying a partial regulation of this metal in the mussels. There was no evidence of any interaction of Cd and Zn in their assimilation by the mussels. These results suggest that mussels are highly responsive, in an element-specific way, to some components of ingested food (e.g., metal concentration), but other food components (such as the biochemical composition of the algae) have little effect on assimilation.     

Effects of oil on behavioral responses to light,pressure and gravity in larvae of the rock crab Cancer irroratus

Cancer irroratus Say larvae (Zoeal Stages I–V and megalopae) were cultured and studied in 0.0, 0.1, and 1.0 ppm concentrations of water-accommodated fractions of No. 2 fuel oil under static conditions. Behavioral changes were monitored in terms of water column responses to various conditions of light, pressure and gravity. Results showed significant (F=206.12, P<0.01) effects of this oil fraction on larval behavior, with the specific response to oil depending upon the concentration, larval stage and the combination of light, pressure and gravity tested. Responses at 0.1 ppm differed from those at 1.0 ppm (F=5.01, P<0.05). Geonegative upward movements in the water column were typically depressed in early-stage larvae and enhanced in late-stage larvae after subjection to oils, showing gravity responses to be greatly affected. Phototactic behaviors were significantly changed by the oil and pressure responses were slightly affected.     

Chelator-induced bioextraction of heavy metals from artificially contaminated soil by mushroom (Coprinus comatus)

This study investigated the potential use of chelator-induced bioextraction of heavy metals from soil by Coprinus comatus in a pot experiment. Two production waves of the mushroom were obtained to determine biomass and metal concentration. The application of ethylenediaminetetraacetic acid (EDTA) or nitrilotriacetate (NTA) slightly inhibited the growth of C. comatus, but significantly enhanced the accumulation of heavy metals in fruiting bodies compared with the control. The highest concentrations of Pb, Cu and Cd reached 900.60, 783.61 and 23.64 mg·kg^?1 in a single pot, respectively. However, application of citric acid (CA) had no effect on metal uptake. Moreover, chelators applied to soil after fructification increased the dry biomass and metal concentration in fruiting bodies compared with those applied before sowing mycelia. EDTA was more efficient for inducing metal uptake by C. comatus than NTA or CA, and split applications of EDTA after fructification resulted in the highest total metal uptake by mushroom, i.e. 19.08±2.84, 17.57±0.69 and 0.55±0.06 mg for Pb, Cu and Cd, respectively, which were 130, 12 and 5 times values obtained with the control. Interestingly, many mushrooms turned blue after soil had been treated with chelator, indicating that these mushrooms are rich in Cu.     

Low uptakes of Cd,Cu, and Zn in Dugesia japonica,a freshwater planarian with higher tolerance to metals

Although a freshwater planarian is proposed as a potential model for studying toxicities of environmental pollutants, they are less sensitive to metal exposures, compared to other freshwater invertebrates. We hypothesised that the metal uptake is low in treated planarians, which may lead to their higher tolerance to metals. The acute toxicities of Cu and Zn to Dugesia japonica were determined. The 24- and 48-h median lethal concentrations were 4.50 and 3.46?mg?L^?1, respectively, for Cu, and 41.97 and 37.79?mg?L^?1, respectively, for Zn. Accordingly, combining with the data on Cd in our previous study, higher tolerance of planarians to metals was revealed. Also, tissue levels of Cd, Cu, and Zn in treated D. japonica were determined, and their dissolved uptake rate constants (k₁) were calculated. Results showed that bioaccumulations of these metals in D. japonica were, indeed, lower than that in other freshwater invertebrates having higher susceptibilities to these metals.     

Effects of the juvenile hormone mimic ZR-515 (Altosid®) on larval development of the mud-crab Rhithropanopeus harrisii in various salinities and cyclic temperatures

Effects of 0.01, 0.1 and 1.0 ppm methoprene (Altosid^®: ZR-515), a juvenile hormone (JH) mimic which shows high activity against some economically important insect pests, especially Diptera, were tested on larvae of the mud-crab Rhithropanopeus harrisii (Gould) (Brachyura: Xanthidae) from hatching to the first crab stage under optimum and stress conditions of a number of salinities and cyclic temperatures. There was a significant reduction in survival of zoeal larvae with increasing concentrations of methoprene in nearly all combinations of salinity and temperature. On the average there was 9% less survival in the 0.01 ppm concentration of methoprene than in the control, and in the 0.1 ppm concentration the survival was further reduced by another 16%. At 1.0 ppm methoprene no larvae survived beyond the first zoeal stage under optimum conditions or under stressful combinations of salinity and temperature. Except at 0.2 ppm in 27.5% S, survival of the megalopa was not significantly reduced in 0.01 or 0.1 ppm methoprene in any salinity or temperature, although the percentage of abnormal megalopa increased under stress conditions. The first zoeal stage was the most sensitive of the larval stages to methoprene as well as to salinity and temperature stress. The duration of zoeal development was significantly lengthened with an increase in concentration of methoprene under nearly all conditions of salinity and temperature. The JH mimic had, however, no significant effect on the duration of megalopa development. A significant synergism between methoprene, salinity and temperature was not observed. It can be concluded from the results that methoprene does not inhibit metamophosis of R. harrisii larvae at the 0.1 ppm level or lower. Reduction in survival of zoeal stages and increased duration of zoeal development with increasing concentrations of methoprene are presumably related to stress.     

Uptake of seven metals by two macrophytes species: potential for phytoaccumulation and phytoremediation

Aquatic macrophytes can be used in the studies of quality of water ecosystems and in monitoring of metals and other pollutants. The aim of this study was to assess concentration levels, accumulation and distribution of seven metals in selected plant parts of Typha angustifolia L. and Iris pseudacorus L., in comparison with sediment and water samples of a reservoir. Metal content in the samples was determined by optical emission spectrometry (ICP-OES iCAP 6500). The concentrations of all examined metals were higher in the sediment than in the water samples. In plants, metal concentrations depended on plant species and organs. The roots/rhizomes were primary organs for metal concentration and accumulation. T. angustifolia L. accumulated Mn and Cu, and I. pseudacorus L. accumulated Cd and Cu in the fruits. T. angustifolia L. hyperaccumulated As. The values of enrichment coefficients and translocation factors were: 0 to 3.31 and 0 to 2.39, respectively. The plant species investigated absorb, translocate and accumulate metals in their organs differently, which provides advantages in combining them for remediation of wasted aquatic ecosystems.     

The uptake and translocation of selected elements by cole (Brassica) grown using oasis soils in pot experiments

Pot experiments were conducted on cole (Brassica) grown in soils jointly treated with traces of two heavy metals cadmium (Cd) and zinc (Zn). As the concentration of heavy metals in the soil increased, the uptake of these metals by the plants rose. However, the ratio of heavy metal concentration in soil to uptake by plants increased at a slower rate. Bioavailability of heavy metals considered between the roots and soil using non-linear regressions was shown to be statistically significant. Similarly, the bioavailability of these two heavy metals between leaves and roots using a linear regression was also statistically significant. The bioconcentration factors (BCFs) for Cd and Zn were 0.282 and 4.289, respectively. Significant variation of BCF with the heavy metal bioavailability in soil was noted from non-linear models. The transfer factors (TFs) were 4.49 for Cd and 1.39 for Zn. The Zn concentration in leaves under all treatments did not exceed threshold set standards, but Cd levels exceeded these standards when the concentration of Cd in the soil was more than 1.92 mg kg^?1 dry weight (dw). Data indicate that cole (Brassica) is not a suitable crop for oasis soils because of plant contamination with heavy metals, especially Cd.     

Heavy metal action on transintegumentary absorption of glycine in two annelid species

Absorption of ¹⁴C-glycine from ambient sea water across the body surface of the oligochaete Enchytraeus albidus Henle was, after 6 h preincubation, significantly reduced in the presence of 0.1 to 0.15 ppm mercury, 0.25 ppm copper, 1.5 ppm silver, and 2 ppm cadmium. Addition of heavy metal salts reduced maximum uptake rates (V _max ), without affecting transport constants (K _t ). Influx of ¹⁴C-glycine remained unchanged in the presence of up to 10 ppm aluminium, chromium, iron, lead, molybdenum, vanadium, and zinc. Effects of up to 150 ppm nickel, manganese, cobalt and selenium were negligible. Inhibition of glycine absorption by mercury and cadmium in the polychaete Nereis diversicolor Müller is almost identical with results presented for E. albidus. Transintegumentary solute absorption in soft-bodied marine invertebrates obviously represents a suitable biological function for studies on heavy metal toxicity. The close relationship between rates of heavy metal absorption, inhibition of transintegumentary glycine uptake, and acute toxicity is discussed.     

The toxicity of heavy metals to embryos of the American oyster Crassostrea virginica

The acute toxicity of 11 heavy metals to embryos of the American oyster Crassostrea virginica was studied and the concentrations at which 50% of the embryos did not develop were determined. The most toxic metals and their LC₅₀ values were mercury (0.0056 ppm), silver (0.0058 ppm), copper (0.103 ppm) and zinc (0.31 ppm). Those metals that were not as toxic and their LC₅₀ values were nickel (1.18 ppm), lead (2.45 ppm) and cadmium (3.80 ppm). Those metals that were relatively non-toxic and their LC₅₀ values were arsenic (7.5 ppm), chromium (10.3 ppm) and manganese (16.0 ppm). Aluminum was non-toxic at 7.5 ppm, the highest concentration tested.     

Comparison of the bioavailability of Cr and Fe bound with natural colloids of different origins and sizes to two marine bivalves

Recent studies have demonstrated the significant role of colloidal microparticles or macromolecules in the biogeochemical cycling of trace metals in aquatic environments. In this study, the influences of different colloidal organic carbon (COC) concentrations, colloidal sizes and colloidal origins (estuarine vs coastal) on the bioavailability of two trace metals (Cr and Fe) to the green mussel Perna viridis and the clam Ruditapes philippinarum were examined under laboratory conditions. Natural colloids were isolated by cross-flow ultrafiltration and were radiclabeled with ⁵⁹Fe and ⁵¹Cr before being exposed to the mussels and clams. The uptake of colloid-bound Cr and Fe was compared with the uptake of low molecular weight complexed metals (<1 kDa). Both natural colloid-bound Cr and Fe were bioavailable to the green mussels and clams. The uptake of both colloidal Cr and Fe by the two bivalves was much higher than that of their counterparts in a low molecular weight fraction, implying that colloidal binding enhanced considerably the bioavailability of Cr and Fe to the bivalves. The magnitude to which Cr uptake was enhanced, due to its binding with colloids, was much greater than that of Fe. There was no significant difference in the measured dry weight concentration factor of the metals between the two COC concentrations. Similarly, the COC concentration did not influence metal uptake when all the experiments were considered together. There was generally no major difference in the metal bioavailability between the two different sizes of colloids isolated from the coastal waters (1–10 kDa and 10 kDa-0.2 μm), whereas metals bound with the larger size colloids isolated from the estuarine waters were more bioavailable than metals bound with the smaller size colloids. The bioavailability of Cr and Fe bound with the colloids from estuarine waters was generally lower than those bound with colloids from the coastal waters. This study demonstrated that the geochemical properties of colloids (origin) and the chemical properties of metals are critical in affecting the bioavailability of colloid-bound metals to marine bivalves. Published online: 21 June 2002     

Acclimation and tolerance of Artemia salina and Ophryotrocha labronica to cooper sulphate

The brine shrimp Artemia salina L. and the polychaete worm Ophryotrocha labronica La Greca and Bacci were acclimated in sea water with copper sulphate at concentrations of 0.1, 0.05, and 0.025 ppm Cu⁺⁺, for 3 and 2 generations, respectively. Both adults and larvae of A. salina showed a greater tolerance to 1 ppm Cu⁺⁺ after acclimation compared to controls of the same age, although this tolerance diminished in successive generations. The acclimation effect was less marked in O. labronica. In both species, tolerance to 10 ppm Cu⁺⁺ upwards was not enhanced. Growth-rate inhibition and an adverse effect on reproduction was observed, in some instances in direct relationship to the acclimation concentration. It is suggested that, in A. salina, a certain tolerance to copper may be acquired through exposure to low concentrations.     

Toxicity of zinc,cadmium and copper to the shrimp Callianassa australiensis. III. Accumulation of metals

Callianassa australiensis (Dana) that survived 14 d acute lethality studies were analysed to determine the concentrations of zinc, cadmium and copper in the whole shrimp and in various parts of the body. Using regression analysis, the influence of each metal upon the uptake of the others was studied. Zinc and cadmium appeared to enhance the uptake of each other. In a mixture of zinc and copper, the uptake of zinc was enhanced and that of copper was inhibited. In a mixture of cadmium and copper, the uptake of copper was inhibited by the presence of cadmium, but cadmium uptake was unaffected in the presence of copper. In a mixture of all three metals, similar effects were observed except that zinc and copper, occurring together, appeared to have no effect upon cadmium uptake. Additional 14 d experiments with cadmium suggested that accumulation of this metal was a function of metal concentration in the water and of duration of exposure. The whole shrimp cadmium concentration also appeared to be a function of the size of the shrimp. The variation in concentration factors is described and the need for further research on the effects of combinations of metals on various organisms is emphasized.     

Trace metal ingestion and assimilation by the green mussel <Emphasis Type="Italic">Perna viridis </Emphasis>in a phytoplankton and sediment mixture

We examined trace metal ingestion and assimilation (Cd, Se, Zn) by the green mussel Perna viridis in a mixture of diatoms and sediment at concentrations below and above the pseudofeces production levels. Dual gamma radiotracers (¹⁰⁹Cd, ⁶⁵Zn) were used to investigate particle selection on marine diatoms and sediments. The diatom (Thalassiosira weissflogii) was radiolabeled with ¹⁰⁹Cd, and the natural sediment was radiolabeled with ⁶⁵Zn. By comparing the ratios of ¹⁰⁹Cd:⁶⁵Zn in the particle mixture, mussel tissues and pseudofeces within a short-term exposure period (35 min), the results demonstrated that the green mussels were able to selectively ingest the diatom particles at a high particle load. Efficiency of selection for nutritious particles (e.g. diatoms) increased with increasing ratio of sediments in the particle mixture. Pseudofeces contained a higher ratio of sediments relative to that in the feeding suspension. No major particle selection was observed at concentrations below the level for pseudofeces production. The assimilation of Cd, Se and Zn by the green mussels was quantified using a pulse-chase feeding technique. The assimilation of Se and Zn by the green mussels from ingested diatoms was reduced with the presence of sediment within the mussel gut, presumably due to the resorption of metals onto the sediment, leading to a quicker passage of metals through the digestive tract and a lower proportion of metals subjected to intensive digestion. In contrast, the presence of diatoms did not significantly affect metal assimilation from ingested sediment. A significant correlation between metal assimilation efficiency and metal gut passage time was also observed. Metal assimilation by the green mussels appeared to be little dependent on the particle concentration in seawater. Our study suggests that particle selection may potentially alter metal influx from ingested food sources, particularly at high particle concentrations. Selective feeding of nutritious particles, coupled with a high assimilation efficiency from these ingested particles, may increase metal influx into mussels from the dietary phase.     

Essential and non-essential heavy metals in skin and muscle tissues of franciscana dolphins (Pontoporia blainvillei) from the southern Argentina coast

Franciscana dolphin, Pontoporia blainvillei, is a small and ‘vulnerable’ cetacean, which exhibits coastal marine habits according to the IUCN (2008). The aim of this work was to determine the presence of essential (Zn and Cu) and non-essential (Cd, Pb, Cr and Ni) heavy metals in skin (n=33) and muscle (n=36) tissues of franciscana dolphins from southern Buenos Aires, establishing the influence of biological parameters on the accumulation of these pollutants. Histological standardised methods were used to determine both age and sexual maturity of the dolphins. Heavy metal concentrations were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Zn was 8-fold higher than Ni in the skin. Zn was significantly affected by the age of the specimens and might be influenced by the state of body condition. Ni showed a behaviour pattern similar to that of non-essential heavy metals. The relationship between Ni and Zn concentration determined in skin and muscle might provide a tool for studying the general condition of endangered marine mammal species such as franciscana dolphins.     

Acclimation and tolerance of Artemia salina to copper salts

The brine shrimp Artemia salina L. was acclimated in sea water with cupric chloride, acetate, carbonate, and sulphate, each at concentrations of 0.1, 0.05 and 0.025 ppm Cu⁺⁺, together with sea water controls. Growth inhibition was observed in all four compounds, generally in direct relationship to the concentration. It was least in sulphate, and increased progressively in chloride, acetate and carbonate in that order. No inhibition however was observed in carbonate at 0.025 ppm Cu⁺⁺. In toxicity tests, 2-week old larvae from each solution were exposed to concentrations of 10, 7.5, 5, 2.5 and 1 ppm Cu⁺⁺ of the same compounds, together with unacclimated larvae of the same age. Similar tests were held with 6-week old adults acclimated (a) in 0.1 ppm Cu⁺⁺ (chloride, acetate and sulphate) using the same concentrations and (b) in 0.5 ppm Cu⁺⁺ (carbonate), using 150, 125, 100, 75, and 50 ppm Cu⁺⁺. Toxicity to unacclimated larvae and adults differed with the compounds, carbonate being the least toxic, followed by sulphate, chloride and acetate in increasing order. Larvae acclimated in chloride (0.025 ppm Cu⁺⁺) and sulphate (0.1 and 0.5 ppm Cu⁺⁺) showed an increased tolerance to 1 and 2.5 ppm Cu⁺⁺ compared to untreated controls. Tolerance was not enhanced from 5 ppm Cu⁺⁺ upwards. In both compounds, adults acclimated in 0.1 ppm Cu⁺⁺ showed an increased tolerance to concentrations between 1 and 7.5 ppm Cu⁺⁺ compared to controls. Larval mortality in carbonate was below 50% in all test solutions. Adults acclimated at 0.5 ppm Cu⁺⁺ showed an increased tolerance to 50 ppm Cu⁺⁺ compared to controls. Considerable precipitation occurred with the high levels of this compound, thus effecting the final concentrations. No acclimation effect was observed in acetate for either larvae or adults. It is suggested that in A. salina, copper toxicity depends on the particular form of the metal, and that this difference is also evident in growth inhibition and in the potential acquisition of increased tolerance through exposure to low concentrations.     

Effect of Pb,Cd and Cu on survival and development of Culex quinquefasciatus (Diptera: Culicidae)

ABSTRACT

The present research aimed to determine the lowest levels of three heavy metals (Pb, Cd and Cu) to which the larvae of Southern House Mosquito, Culex quinquefasciatus are susceptible in water. The study also aimed to investigate the effects of these heavy metals on the development of Cx. quinquefasciatus at concentrations set by Pakistan Environmental Protection Agency (Pak-EPA) as permissible levels for liquid industrial effluents. The 2nd instar larvae of Cx. quinquefasciatus were exposed to different concentrations of Pb, Cd and Cu and their effects on oviposition preference, egg hatching rate and larval development were studied. The LC₅₀ values of Pb, Cd and Cu were 12.6, 6.3 and 2.6?ppm, respectively. Gravid female mosquito adults deposited a significantly lower number of egg rafts in containers containing 0.50?ppm Pb or 1.0?ppm Cu in water. Each of the heavy metals in water resulted in significantly (p?<?0.05) lower egg hatching rate, prolonged time to pupation, lower pupation rate, prolonged time to adult emergence, lower adult emergence rate and higher female to male ratio. It is concluded that the 2nd instar larvae of Cx. quinquefasciatus are susceptible to Pak-EPA permissible levels of Pb, Cd and Cu in municipal and liquid industrial effluents.     

Accumulation of cadmium by Artemia salina

The relative importance of accumulation of cadmium by Artemia salina (L.) directly from solution and from ingested food has been studied at 3 cadmium concentrations (0.1, 1 and 10 ppm) under controlled experimental conditions. At each cadmium concentration, A. salina were exposed to cadmium in 4 ways; in solution; in solution in the presence of latex food particles; in solution with cadmium-rich Dunaliella tertiolecta as a food source; and to cadmium-rich D. tertiolecta alone. Net accumulation of cadmium by A. salina continued throughout 5 days exposure under all 4 conditions. When the brine shrimp were removed to cadmium-free conditions, their accumulated cadmium concentrations declined and levelled off to a stabilised plateau after 10 days. From consideration of these stabilised levels it was shown that at least 30% of cadmium accumulation directly from solution occurs via uptake through the alimentary tract. The ratio of cadmium accumulated from solution to cadmium accumulated from food was found to be 1:4.9, 1:6.7 and 1:1.1 at 0.1, 1 and 10 ppm Cd exposure, respectively. At lower cadmium exposures uptake from food is the major route for cadmium accumulation, but at higher exposures the cadmium-saturated food source displaced cadmium-rich water from the gut and therefore actually inhibited cadmium accumulation. This study, therefore, concludes that the food chain will be the major source of cadmium as long as the previous trophic level has the ability to accumulate the metal to such an extent as to make it more available to the consumer than by direct uptake from seawater.