Growth of Uronema marinum in chemically defined medium

A strain of the marine hymenostome ciliate Uronema marinum was isolated in axenic culture. This strain, designated PW2, was cultivated in a chemically defined medium containing 17 amino acids, 4 nucleotides, 5 fatty acids, stigmasterol, 8 growth factors and an artificial sea water. Increased populations were observed when either phosphatidylinositol or Tween 80 were included in the medium. The vitamins thiamine, riboflavin, pyridoxal, nicotinamide, folic acid and pantothenate were required by U. marinum PW2. No requirement could be demonstrated for exogenous thioctic acid or biotin, although growth was diminished in their absence. The amino acid and nucleotide requirements were found to be higher than the levels reported for other ciliates. This strain was found to be euryhaline, with maximum growth observed in media of specific gravity 1.007, corresponding to approximately 25% sea water. Although no requirement could be demonstrated for Fe, Zn, Mn or Cu, high levels of these metals were observed to be toxic. Growth was observed over a pH range of 6.6 to 8.3, with an optimum observed near 7.3.     

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.     

The common mussel Mytilus edulis as an indicator of pollution by zinc,cadmium, lead and copper. I. Effects of environmental variables on uptake of metals

The net uptake of zinc, cadmium, lead and copper by the common mussel Mytilus edulis (L.) exposed to different conditions was investigated with a view to using this species as an indicator of contamination of the marine environment by these metals. The variables studied were season, position of the mussel in the water column, water salinity, water temperature, and the simultaneous presence of all four metals. Each of these 5 variables affected the net uptake of some or all of the metals studied under some conditions. Seasonal variation in concentrations of zinc, cadmium and copper was found in samples collected at three separate locations. The relationship of seasonal variation to tissue weight and absorption route of the metals is discussed. Near to freshwater inputs of trace metals, the concentrations of zinc, cadmium and lead in mussels were found to vary according to the depth at which the mussels were collected; in summer when freshwater run-off is less, this effect was absent. Low salinities did not affect the net uptake of zinc by mussels, but increased the net uptake of cadmium and decreased that of lead. Low temperatures had no effect on the net uptake of zinc or lead; the net uptake of cadmium was unaffected by low temperatures at high salinities but was decreased by low temperatures at low salinities. The presence of the other metals had no effect on the individual net uptake of either zinc, cadmium or lead. A sampling programme was devised to eliminate the effects of these environmental variables and to allow the use of M. edulis as an indicator of zinc, cadmium and lead in marine and estuarine environments. In contrast to the other metals, the net uptake of copper by the mussel was extremely erratic, and was affected by salinity and temperature changes and by the presence of the other metals and changes in their relative concentrations. The effects of other metals on the net uptake of copper cannot be easily eliminated or allowed for; it is, therefore, suggested that the mussel should not be used as an indicator of copper in the marine environment.     

Decline in metallophytes in tertiary polluted floodplain grasslands in the Netherlands: experimental evidence for metal and nutritional changes in soil as driver factors

Metallophyte vegetation along the River Geul has been almost completely replaced by grasses during the last decades. Field investigations indicated that this was accompanied by higher alkalinity and phosphate availability in the soil, related to the closure of the metal industry and intensification of agricultural practices. An experiment with a full factorial design for phosphate and zinc availability indicated that the metallophytes Silene vulgaris and Thlaspi caerulescens did not grow on zinc-poor soils, irrespective of phosphate availability. The grass Holcus lanatus performed well on phosphate-rich soil, irrespective of zinc availability. An experiment with zinc-poor and zinc-rich floodplain soils confirmed the high zinc demand of the metallophytes T. caerulescens and Armeria maritima and the zinc independence of H. lanatus. A third experiment indicated that a reduced zinc availability due to liming affected only the metallophyte T. caerulescens; it had no effect on the growth of the grass Festuca rubra. This means that increasing alkalinity leads to a decrease in zinc availability, limiting the growth of at least some metallophyte species. An increase in phosphate availability stimulates growth in more competitive fast-growing grasses under zinc-rich as well as zinc-poor conditions.     

The use of algae to control heavy metals in the environment

Aqueous effluents from a lead mining and milling operation located in southeastern Missouri, USA, caused a degradation of stream quality despite treatment by a large tailings pond. The receiving stream was choked with algal mats which accumulated unexpectedly large amounts of manganese, lead and zinc. A wastewater treatment system was designed to utilize algae and benthic macrophytes to remove metals from the tailings pond effluent. The system has proved successful and water quality in the receiving stream has been improved to drinking water standards.Experiments were conducted to understand more fully the phenomenon of heavy metal accumulation by algae. Radionuclides (²¹⁰Pb,²⁰³Hg,⁶⁵Zn,¹⁰⁹Cd) were used in conjunction with commercially available microculture apparatus to screen several species of algae for heavy metal accumulation. It was found that all species of algae studied concentrated mercury, green algae were more efficient accumulators of cadmium than blue-green algae, one alga (Chlamydomonas) proved best at removing lead from solution and no alga studied removed zinc.     

The Influence of Temperature and Salinity Upon the Acute Toxicity of Heavy Metals to the Banana Prawn (Penaeus merguiensis de Man)

Bioassays were conducted to determine the effects of temperature and salinity on the acute toxicity of mercury, copper, cadmium, zinc, nickel and lead to juvenile banana prawns (Penaeus merguiensis de Man). Tests were conducted at all combinations of 35, 30 and 20°C with 36 and 20° salinity over 96 h. The general rank order of metal toxicity was Hg > (Cu, Cd, Zn) > Ni > Pb. The toxicity of all metals increased with increased temperature. This was most noticeable in the high salinity treatments, particularly for copper and zinc. Salinity appeared to influence the toxicity of all metals tested although significant differences were only found for copper and lead at 20°C. At this temperature prawns were markedly more susceptible to both metals in low salinity sea water. The data are compared with lethal concentrations found for other crustaceans and are discussed in relation to existing water quality criteria.     

Heavy Metal Concentrations in Sea Urchin Tissues From Egypt,Ireland and United Kingdom

Abstract

Sea urchins (Paracentrotus lividus) were collected from the Mediterranean coast off Alexandria, Egypt and the Atlantic coast of Ireland to the west of Galway. Samples of another urchin species, Psammechinus miliaris, were collected from the entrance to Southampton Water, U.K. Both the Alexandria coast and Southampton Water receive domestic and industrial waste water inputs whilst the western Irish coast is relatively unpolluted.

Sampled animals were dissected to separate coelomic fluids, Aristotle's lantern, gonads and tissue (digestive tract plus connective tissue). the concentrations of heavy metals (cadmium, copper, lead, nickel and zinc) in the different parts were measured using flame atomic absorption spectroscopy.

Many levels of heavy metals in the different parts were similar in specimens taken across the wide range of sites and the two species. A notable exception was the high level of copper (33 μg g^?1 dry wt.) and zinc 328 μg g^?1? dry wt.) in urchin tissue from Southampton Water.

The metal concentrations in the gonads of Paracentrotus lividus are of particular interest because of human consumption of this species. the highest levels of copper (3.3–5.2 g^?1? dry wt.) and zinc (74–181 μ g^?1? dry wt.) dry wt.) in gonads were found in the samples from Egypt. Data from this study are compared with other results reported from the Mediterranean.

A simple, short term, elevated water column copper uptake experiment was undertaken with Paracentrotus lividus which showed an increase in gonad concentrations of this element.     

Metal levels in some benthic organisms of Haifa Bay,mediterranean (Israel)

Benthic organisms revealed enhanced uptake of mercury from polluted surface sediments (in the vicinity of a chlor‐alkali plant) which were enriched in mercury by up to 148 times relative to sediments from an unpolluted area. There is a strong correlation between the concentrations of mercury in the benthic organisms and sediments. No correlation was found between cadmium, lead, copper and zinc levels in the benthic fauna populations and the concentrations of these metals in the sediments. Ranges of concentrations (μg/g wet wt.) in the whole soft tissues varied: Hg, <0.005–3.31; Cd <0.018–1.99; Pb, <0.025–1.56; Cu, 0.242–28.8; and Zn, 9.75–310.2. The three gastropod molluscs show higher metal concentrations than do the bivalves.     

Determination of concentration of heavy metals in two common fish species from asa river,ilorin, nigeria

Concentrations of some heavy metals in Tilapia zilli (Tilapia) and Synodontis membrane (Catfish), the two common fishes from Asa River Ilorin, Nigeria have been determined. Manganese, zinc, iron, and lead, were present at appreciable concentrations in the tissues of the two species while cadmium, mercury, and nickel, were found to be less than 0.01?ppm. Concentrations of metals were highest downstream than at upstream locations. Mean concentrations of Mn in Tilapia, ranged between 0.56?ppm at the upstream end and 2.69?mg/kg of fresh weight at the downstream end. Pb, Zn, and Cr ranged between 4.05 and 5.59?mg/kg of fresh weight, 0.09 and 1.16?ppm, 5.62 and 11.15?ppm, and 0.09 and 0.13?ppm respectively. In the Catfish, Mn, Fe, Zn, and Cr ranged between 0.62 and 0.78?ppm, 3.79 and 8.79?ppm, 0.78 and 1.57?ppm, 7.30 and 15.15, and 0.23 and 0.35?ppm respectively. Heavy metals except lead did not pose any health risks in human since the calculated probable amounts being ingested by an average adult (50?kg average weight) per day were lower than WHO maximum recommended value of intake. However, the level of lead was higher than WHO limit and this could render inedible the fishes from this catchment river.     

Effects of copper and zinc on two planktonic ciliates

The interactive effects of copper and zinc on two estuarine planktonic ciliates, Favella sp. and Balanion sp., were determined in seawater media in which the free metal ion activities were controlled by nitrilotriacetic acid (NTA) trace metal ion buffer systems. Cupric ion activities of 10^-10 M caused abnormal motility in both ciliates in shortterm (5 h) tests, and cupric ion activities as low as 10^-12.8 M decreased the growth rates of both species in longer-term experiments. In the short-term tests, zinc ion activity by itself did not affect the motility of the ciliates, but there were significant interactions between copper and zinc. In the longer-term experiments, the growth of Favella sp. was optimal at the lowest cupric ion activity (10^-13 M) and the two lowest zinc ion activities (10^-12 and 10^-13 M) and the two lowest zinc ion activities (10^-12 and 10^-11 M), and copper and zinc inhibited growth at activities above these values. By contrast, optimal growth rate of Balanion sp. occurred at the highest zinc ion activity (10^-10 M) and the lowest cupric ion activities (10^-13 to 10^-12 M) and growth rate was reduced at zinc ion activities 10^-11 M. There was an antagonism between copper and zinc which was particularly pronounced in Balanion sp.Contribution No. 5871 from the Woods Hole Oceanographic Institution     

Chromosome damage in individuals exposed to heavy metals†

Testing the mutagenic activity of environmental pollutants has become an important area of modern environmental science and prophylactic medicine. The most suitable method for short‐term mutagenicity testing on man, at present, are chromosome studies on somatic cells of exposed individuals. Mutation types analyzed by such studies are of high practical relevance as indicator system of genetic damage induced in man under in vivo conditions. A rather large series of such studies has been dedicated to the action of heavy metals on individuals contacted with these metals under therapeutic, ecological or occupational conditions or by intoxication. Lead, cadmium, chromium, nickel, mercury, zinc and other metals as well as their compounds have been under study. Analyses of that kind, of course, are hampered by difficulties with the distinct estimation of the actual load as well as unclear conditions of exposition, e.g. simultaneous exposition to different metals.

Results obtained till now arouse some suspicion of a direct or indirect mutagenic activity in man by certain chromium and platinum compounds, arsenic, mercury, and combinations of lead with other heavy metals (cadmium, zinc, arsenic, antimony, etc.). Life style, above all smoking habits, well may act comutagenic. In most cases, however, mutagenic activity of metals and metal compounds apparently is clearly superposed by their toxic activity. In specific cases, chromosome studies also may contribute to discover sources of ecological exposition and to monitor occupational load by heavy metals.     

Mechanism of toxicity of zinc to the marine diatomNitzschia closterium

The effect of zinc on cell division, photosynthesis, ultrastructure, respiration, ATP levels, mitochondrial electron-transport chain (ETC)-activity, total thiols and glutathione in the marine diatomNitzschia closterium (Ehrenberg) W. Smith was investigated. Although 65µg Zn 1^–1 halved the cell division rate, photosynthesis and respiration were unaffected by zinc concentrations up to 500µg Zn 1^–1. Most of the zinc associated with the cells was bound at the cell surface, with only 3 to 4% of this extracellular zinc penetrating the cell membrane. Once inside the cell, zinc exerted its toxicity at a number of sites. Increased ATP production and ETC activity were observed in zinc-treated cells. Zinc also enhanced cellular thiols (SH) and total glutathione, and zinc toxicity was reversible by the addition of thiol compounds such as cysteine. Zinc-thiol binding may be a detoxification mechanism for the cell. It is suggested that increased ATP production may provide the energy required for increased glutathione synthesis at the expense of other energy-requiring processes including cell division. The mechanisms of toxicity of ionic zinc and copper toN. closterium were compared.     

A Screening-Level Assessment of Lead, Cadmium, and Zinc in Fish and Crayfish from Northeastern Oklahoma, USA

The objective of this study was to evaluate potential human and ecological risks associated with metals in fish and crayfish from mining in the Tri-States Mining District (TSMD). Crayfish (Orconectes spp.) and fish of six frequently consumed species (common carp, Cyprinus carpio; channel catfish, Ictalurus punctatus; flathead catfish, Pylodictis olivaris; largemouth bass, Micropterus salmoides; spotted bass, M. punctulatus; and white crappie, Pomoxis annularis) were collected in 2001--2002 from the Oklahoma waters of the Spring River (SR) and Neosho River (NR), which drain the TSMD. Samples from a mining-contaminated site in eastern Missouri and from reference sites were also analyzed. Individual fish were prepared for human consumption in the manner used locally by Native Americans (headed, eviscerated, and scaled) and analyzed for lead, cadmium, and zinc. Whole crayfish were analyzed as composite samples of 5--60 animals. Metals concentrations were typically higher in samples from sites most heavily affected by mining and lowest in reference samples. Within the TSMD, most metals concentrations were higher at sites on the SR than on the NR and were typically highest in common carp and crayfish than in other taxa. Higher concentrations and greater risk were associated with fish and crayfish from heavily contaminated SR tributaries than the SR or NR mainstems. Based on the results of this and previous studies, the human consumption of carp and crayfish could be restricted based on current criteria for lead, cadmium, and zinc, and the consumption of channel catfish could be restricted due to lead. Metals concentrations were uniformly low in Micropterus spp. and crappie and would not warrant restriction, however. Some risk to carnivorous avian wildlife from lead and zinc in TSMD fish and invertebrates was also indicated, as was risk to the fish themselves. Overall, the wildlife assessment is consistent with previously reported biological effects attributed to metals from the TSMD. The results demonstrate the potential for adverse effects in fish, wildlife, and humans and indicate that further investigation of human health and ecological risks, to include additional exposure pathways and endpoints, is warranted.This study was conducted by the Columbia Environmental Research Center (CERC) of the U.S. Geological Survey (USGS) and cooperating organizations and government agencies. All field and laboratory procedures conformed to the “Guidelines for the use of fishes in research” of the American Fisheries Society (AFS), Institute of Fishery Research Biologists (AIFRB), and American Society of Ichthyologists and Herpetologists (ASIH) Use of Fishes in Research Committee (AFS, AIFRB, and ASIH 2004), and with all USGS and CERC guidelines for the humane treatment of test organisms during culture and experimentation. Use of trade names does not constitute USGS or U.S. government endorsement.     

Humic substances. Part II†: Photophysical,photochemical and free radical characteristics

The effects of mercury (HgCl₂) on cell population, chlorophyll a concentration and rates of photosynthesis and excretion were investigated in the phytoplanktonic species Dunaliella minuta in laboratory cultures. Mercury, above 25ppb inhibited both cell population and chlorophyll a concentration approximately to the same extent, whereas the photosynthetic rate was inhibited to a significantly lesser degree. Although, the total photosynthetic rate of the tested organism was reduced, above a threshold concentration, the photosynthetic activity was not reduced under these conditions, but it was in fact significantly greater than that in the control culture. This may suggest that in D. minuta the inhibitory effect of mercury is primarily on cell division rather than cellular photosynthesis, which is enhanced by the fact mercury caused a significant increase of the mean cell volume. Mercury, also, decreased the growth rate and final cell yield. The excretory rate was markedly increased at concentrations ≥ 250 ppb of mercury, but at lower concentrations it tended to depend more on the physiological state of cells than on mercury concentration. In the different cultures, the photosynthetic activity showed variations which occurred without major changes in the chlorophyll a content per cell, which remained almost constant and independent of variations in cell size and growth conditions.     

海河流域沉积物中典型重金属的生态风险评估及验证

沉积物重金属污染及其生态风险评估日益受到关注,而沉积物质量基准是开展生态风险评估的有力工具。本研究通过物种敏感度分布法(species sensitivity distributions, SSD)和急慢性毒性比(acute to chronic ratios, ACR)推导了镍、铜、锌、镉和铅的沉积物质量基准(sediment quality guideline, SQG)。在获得合理的重金属沉积物慢性毒性数据的基础上,采用S-Logistic模型拟合镍、铜、镉和铅的慢性SSD曲线,采用S-Gompertz模型拟合锌的慢性SSD曲线。得到镍、铜、锌、镉和铅沉积物质量基准低值(sediment quality guideline low value, SQGlow)分别为18.6、69.9、107、1.26和38.4 mg·kg~(-1),应用ACRs,得到相应的沉积物质量基准高值(sediment quality guideline high value, SQGhigh)分别为167、226、556、10.1和384 mg·kg~(-1)。与加拿大和澳大利亚重金属沉积物基准值具有一定的可比性。选择花翅摇蚊(Chironomus kiiensis)、伸展摇蚊(Chironomus tentans)和霍甫水丝蚓(Limnodrilus hoffmeisteri)3种底栖生物作为受试生物,验证基准值对海河流域沉积物重金属毒性的预测能力。结果表明,利用SQGs预测沉积物毒性的总准确率为76.2%,3种底栖生物验证准确率从高至低为:花翅摇蚊>伸展摇蚊>霍甫水丝蚓。     

Comparative study of the age and location dependence of some heavy metals in human hair from two Nigerian cities

The concentration of some heavy metals (lead, zinc and copper) were determined in the scalp hair of children (1–15 year) and active adults (16–40 year) in two Nigerian cities. The levels of zinc were found to be higher in children than in the adult population. There was a significant difference (P?=?0.05) between the two age groups. The levels of copper were all within the same range for the two age groups and independent of location. The levels of lead were generally higher in adults than in children. However, there was no significant difference (P?=?0.05) in the average concentrations of lead between the children and adult populations of the two cities. The regression analysis indicated a strong correlation (r?=?0.86) between zinc and copper.     

Tissue distribution of Cd,Cu, Zn,Ni, Cr,Pb and Hg in striated heron,Butorides striatus (Aves: Ardeidae), in a fluvial ecosystem

In this study, the striated heron (Butorides striatus), a species that reproduces in the Middle Paraná River floodplain, was examined for lead, cadmium, chromium, zinc, nickel, mercury and copper concentrations, using liver, kidney, muscle, vertebra and feathers. The results showed low exposure to chromium because all tissue samples had concentrations below the limit of detection. Similar results were obtained for nickel and lead, with the exception of vertebra. This might be associated with either long-term exposure to these metals, or it may be that both nesting and wintering areas are non-polluted. Zinc and copper, both essential metals, were found in all tissues and their concentrations were within the ranges reported in the literature. Mercury was also found in all tissues, but at very low concentrations and even at concentrations below those that produce negative effects in several species of birds (e.g. reproductive success, food intake). Studies of this type are needed to interpret the role of organisms within environments impacted by different human activities.     

An assessment of copper,zinc and cadmium contamination and their ecotoxicological effects in O. mediterranea Costa, 1853 (Amphipoda,Talitridae)

This study was conducted to compare metals bioaccumulation in the Talitrid O. mediterranea collected from the banks of Bizerte lagoon. Individuals were exposed to a series of contaminated soil with different concentrations of cadmium, copper, and zinc. Biological and physiological responses were highlighted. Body metals concentrations were measured in the talitrid using flame atomic emission spectrometry. Results showed that after the second week, the mortality increased especially with cadmium exposure, and a mass gain was obtained between weeks for copper and zinc. Furthermore, the concentration factor indicated that O. mediterranea could be considered as a macroconcentrator of copper and zinc. Histopathological analysis showed that the different metals concentrations induced significant changes in the morphology and in the ultrastructural organisation of hepatopancreatic cells. Significant alterations obtained after metals exposure were the increase in the number of the majority cell organelles. Also, heavy metals were present in the form of numerous granules with different size in the cell surface. Furthermore, metals exposure affected the brush border causing the disruption of microvilli filament. Through these results, O. mediterranea could be a good indicator providing measurable responses. It could be an attractive candidate for the biochemical study of heavy metals toxicity in coastal ecosystems.     

Replacement and aging of chloroplasts inStrombidium capitatum (Ciliophora: Oligotrichida)

The planktonic ciliateStrombidium capitatum (Leegaard, 1915) Kahl, 1932 retains functional chloroplasts derived from ingested algal cells. Chloroplast replacement and aging were experimentally investigated in cultured ciliates provided with a cryptophyte (Pyrenomonas salina), a prymnesiophyte (Isochrysis galbana) and a prasinophyte (Pyramimonas sp.) as sources of plastids. All three algae were ingested and chloroplasts from all were retained by the ciliate. Within 15 min of exposure to the cryptophyte, this alga was taken up by the ciliates. Initially, most of the cryptophyte chloroplasts were in intact algal cells in ciliate vacuoles. By 2 h, cryptophyte plastids were commonly found free in the ciliate cytoplasm. WhenS. capitatum was switched from a diet containing cryptophytes to a non-cryptophyte diet, most cryptophyte chloroplasts were diluted out of the ciliates by cell division and/or replaced by non-cryptophyte chloroplasts within 9 h. When the ciliates are not provided with algae, they decrease in size and number. However, the starving ciliate cells contain some chloroplasts for as long as they live (40 h or more). Under these conditions, cryptophyte chloroplasts persist longer than the other chloroplast types. Our observations suggest that chloroplast retention times inS. capitatum depend on the type of chloroplast as well as the availability of phytoplankton containing suitable new chloroplasts, and probably also on the physiological states of the ingested algae and the ciliates. It is interesting that we were not able to grow this ciliate when we provided it only with prey that lacked chloroplasts.Contribution No. 7241 from Woods Hole Oceanographic Institution. This research was supported by NSF grants OCE-8600765 and OCE-8709961 to D.K.S     

Risk assessment of heavy metal contamination in shrimp farming in Mai Po Nature Reserve, Hong Kong

An ecological survey was carried out to determine the sediment concentrations of nutrients and heavy metals and bioaccumulation of heavy metals in fish and shrimp including tilapia (Oreochromis mossambicus×O. nilotica), grey mullet (Mugil cephalus), gei wai shrimp (Metapenaeus ensis) and caridean shrimp (Macrobrachium nipponensis) in the traditional tidal shrimp ponds (gei wais) of Mai Po Nature Reserve, Hong Kong. The sediments collected from the landward sites contained higher nutrient contents, as well as zinc (Zn), chromium (Cr), copper (Cu), nickel (Ni) and cadmium (Cd) than those collected from the seaward sites, but vice versa for lead (Pb) and mercury (Hg). However, the concentrations of all metals were exceptionally high in the two sites located outside the reserve, suggesting that waters from Deep Bay might be the possible source of metal contamination affecting the reserve. All metals studied seemed to accumulate in the viscera of fish. Body size was the determining factor for the accumulation of heavy metals in caridean shrimp and gei wai shrimp but not fish. Concentrations of the metals studied in tissues of grey mullet and gei wai shrimp were found to be safe for human consumption. Concentrations of Cr in tilapia whole body (0.68–1.10 mg kg⁻¹ wet weight) were close to or over the guideline value of 1 mg kg⁻¹ set by the Food Adulteration (Metallic Contamination) Regulations of Hong Kong. Tilapia flesh and small caridean shrimp collected from gei wais were contaminated by Cr and Pb but still fit for human consumption. Caution is required if large caridean shrimp is to be consumed in large amounts continuously because the concentration of Pb exceeded the maximum permitted concentration (6 mg kg⁻¹). The rather high Cr concentrations in tilapia whole body should not be overlooked as the fish will serve as a food source for migratory birds visiting the site.