Toxicity of cadmium and zinc to Diplostomum spathaceum (Trematoda: Diplostomidae) cercarial survival

The toxicity of cadmium and zinc at concentrations ranging from 0.1 to 10000 microg/l was investigated with cercariae of Diplostomum spathaceum at three temperatures (12, 20, 25 degrees C) and three levels of water hardness (distilled water, soft water, hard water). Under most environmental conditions survival of cercariae was reduced by increasing metal concentration. Increasing water hardness and decreasing water temperature caused an increase in the survival of both control and metal exposed cercariae. However, with decreasing temperature increased survival of metal-exposed cercariae above the control occurred at a number of low metal concentrations. Differences in the relative toxicity of cadmium and zinc to cercariae was dependent on the environmental conditions of exposure. The two heavy metals demonstrated little toxicity to cercariae during the period of maximum cercarial infectivity (0-5 h).The mechanisms of metal toxicity and their effects on cercarial survival are discussed.     

Toxicity of cadmium and zinc mixtures to the decaudized cercarial life span of Diplostomum spathaceum

The effects of cadmium and zinc mixtures at concentrations ranging from 0.1 to 10,000 microg l(-1) on the life-span of decaudized cercarial bodies (cercariae that have shed their tails) of Diplostomum spathaceum (Trematoda: Diplostomatidae) was investigated. Cercariae were exposed to metal mixtures of equal and unequal concentrations, and a low-dose pre-treatment followed by a high-dose exposure mixtures. Metal mixtures demonstrated variable effects on decaudized cercariae either by increasing or reducing their life-span compared to single metal exposures dependent on concentration and the type of mixed metal treatment. Prolonged exposure to equal metal mixtures at low concentrations (0.1-100 microg l(-1)) resulted in a reduction in the life-span of decaudized cercariae at 0.1 and 100 microg l(-1) in those individuals decaudized during the initial 24 h exposure period compared with those decaudized during the final 24 h period of cercarial survival, whilst in controls there was no significant life-span change between the two time periods. Decaudized cercariae which were exposed to low concentrations (0.1-100 microg l(-1)) of equal metal mixtures were also evaluated for their role as an indicator of larval 'fitness' for migrating through the tissues of their target fish host for those individuals decaudized during the initial 24 h exposure period, and demonstrated only a limited change in their life-span compared to control and single metal exposures. The importance of metal mixtures in parasite establishment in the fish host is discussed.     

Toxic effects of cadmium and zinc on the transmission of Echinoparyphium recurvatum cercariae

The toxicity of cadmium, zinc and Cd/Zn mixtures to the transmission of Echinoparyphium recurvatum (Digenea: Echinostomatidae) cercariae into the snail second intermediate hosts was investigated at concentrations ranging from 100 microg l-1 to 10 000 microg l-1 in both soft and hard water. A differential response in the infectivity of metal-exposed cercariae into Lymnaea peregra and Physa fontinalis was demonstrated which was dependent on the snail species being infected. Exposure of L. peregra, P. fontinalis, and L. stagnalis to heavy metals caused a differing susceptibility to E. recurvatum cercariae depending on the snail species being exposed. The mechanism and effects of metal toxicity, together with the importance of the parasite/host strain on cercarial transmission are discussed.     

Changes in survival characteristics of Diplostomum spathaceum cercariae emerged from cadmium-exposed Lymnaea stagnalis

The effect of exposing Lymnaea stagnalis (Gastropoda: Pulmonata), infected with Diplostomum spathaceum (Trematoda: Diplostomatidae), to 100 microg l(-1) cadmium for 7 days on survival characteristics (survival, tail loss, decaudized cercarial life-span) of emerged cercariae was investigated. Exposure of L. stagnalis to cadmium resulted in significantly increased D. spathaceum cercarial survival and an inhibited tail loss compared to controls. The normal parallel relationship which exists over time between decreasing cercarial survival and increasing tail loss in controls was changed in cercariae from cadmium-exposed hosts with an increased proportion of cercarial deaths occurring without tail loss. The decaudized cercarial life-span over the survival period of the cercarial population did not significantly change. However comparisons between individuals decaudized during the initial 24 h time period with those which were decaudized during the final period of cercarial survival showed a significantly altered life span which did not occur in the control population. As a potential indicator of penetration 'fitness' comparisons were also undertaken between control and exposed cercariae decaudized during the initial 24 h time period, which revealed that the decaudized cercarial life-span from the exposed hosts was significantly different from controls. This may have important implications for the ability of cercariae to migrate through the tissues of their target host. The importance and relevance of these results to parasite transmission are discussed.     

Cercarial tail loss in Echinostoma caproni: the influence of in vivo encystment and copper sulphate

Echinostoma caproni tail loss was studied in vitro in the presence of the toxicant copper sulphate (CuSO4) in concentrations ranging from 1 to 10 000 mg l(-1) in standardized artificial spring water (pH 7.4, osmolarity 34 mOsm kg(-1) H2O, Ca(2+) 20 mg l(-1)) at 23 degrees C. Tail loss was also studied in the absence of toxicants during in vivo encystment of the cercariae in juvenile Biomphalaria glabrata. As the concentration of CuSO4 increased, the percentage of cercarial tail loss increased. By 2 h in 10 000 mg l(-1), 1000 mg l(-1) and 100 mg l(-1) CuSO4, 50%, 23% and 13%, respectively, of the cercariae had lost their tails. In the in vivo studies, by 1 h PI, 59+/-5% of cercariae had lost their tails and only 4+/-1% of the cercariae were actively swimming in the multi-well dishes. At 3 h PI, 72+/-3% of the cercariae began to form cysts within the snails.     

Influence of cadmium exposure on the incidence of first intermediate host encystment by Echinoparyphium recurvatum cercariae in Lymnaea peregra

The effect of cadmium exposure of the snail first intermediate host Lymnaea peregra on the incidence of encystment of Echinoparyphium recurvatum (Digenea: Echinostomatidae) cercariae without emergence from the snail was investigated. Exposure to 100 microg l(-1) Cd for 72 h caused a significant increase in the incidence of first host encystment when compared to controls. In addition, autometallographic staining of E. recurvatum daughter rediae and developing cercariae showed that there was metal accumulation within their body tissues. The significance of these findings to parasite transmission in metal-polluted environments is discussed.     

Tributyltin and copper effects on encystment and in vitro excystment of Parorchis acanthus larvae

Effects of tributyltin (TBT) and copper (Cu) on cercariae and metacercariae of the trematode Parorchis acanthus (Digenea: Philophthalmidae) were investigated. Cercariae released by the dogwhelk, Nucella lapillus were maintained in natural seawater (SW) or solutions of TBT or Cu ranging from 0.001-100 microg l(-1) and 1-6 mg l(-1) respectively before they encysted. Over 79% of the cercariae encysted in control and test solutions. Low concentrations of TBT reduced encystment success more than low concentrations of Cu. The percentage of cercariae that formed cysts in the highest concentrations of both pollutants was higher than in the controls, perhaps representing an 'emergency response' to the pollutants. Before being induced to excyst in vitro, metacercariae were left in the heavy metal solutions for 3 weeks. Metacercariae exposed as cercariae to TBT and Cu achieved lower percentage excystment success than those that had encysted in SW. Cyst walls provided greater protection against Cu than TBT. It was concluded that TBT and Cu had a detrimental effect on the larval stages of P. acanthus at the higher concentrations used but the cyst wall afforded an element of protection if formed in unpolluted seawater before the larval stages were subjected to the pollutants.     

Cadmium removal by living cells of the marine microalga Tetraselmis suecica

Cadmium removal by living cells of the marine microalga Tetraselmis suecica was tested in cultures exposed to different cadmium concentrations (0.6, 3, 6, 15, 30 and 45 mg/l). The EC50 for growth was 7.9 mg Cd/l after six days of exposure. The cadmium removed was proportional to the concentration of this metal in the medium and it was dependent on the time of exposure; cultures with higher cadmium concentration removed a higher amount of this metal. In cultures exposed to 0.6 mg/l, T suecica cells removed 98.1% of added cadmium with 0.392 x 10(-6) microg Cd/cell, whereas in cultures with 45 mg/l only 7.7% was removed with 16.052 x 10(-6) microg Cd/cell. The highest amount of cadmium removed per liter of culture was observed in cultures exposed to 6 mg/l, with 3.577 mg/l of cadmium. After six days of incubation, the higher proportion of cadmium was bioaccumulated intracellularly in all cultures except in 45 mg/l cultures, the percentage of intracellular cadmium being always more than 50%. The highest percentage of bioadsorbed cadmium (60.1%) was found in cells of cultures with the highest cadmium concentration (45 mg/l). Furthermore, a relation between intracellular cadmium and the concentration of sulfhydryl groups was observed.     

Alterations of tissue glutathione levels and metallothionein mRNA in rainbow trout during single and combined exposure to cadmium and zinc

The objective of this study was to assess the effects of Cd and Zn exposure of rainbow trout (Oncorhynchus mykiss) on (a) hepatic glutathione (GSH) levels; and (b) hepatic and branchial metallothionein (MT) mRNA expression. Juvenile rainbow trout were exposed to waterborne Cd (nominal concentrations: 1.5 or 10 microg Cd l(-1)), Zn (150 or 1000 microg Zn l(-1)) or Cd/Zn mixtures (1.5 microg Cd l(-1) with 200 microg Zn l(-1) or 10 microg Cd l(-1) with 1000 microg Zn l(-1)). After 14 and 28 days of treatment, hepatic concentrations of total glutathione, oxidized glutathione (GSSG) and cysteine were determined by means of fluorometric high performance liquid chromatography (HPLC). Branchial and hepatic expression of MT mRNA was measured by means of semi-quantitative RT-PCR. Exposure of trout to Zn did not result in significantly elevated tissue levels of Zn, whereas Cd accumulation factors changed significantly with time and concentration. Despite of the absence of Zn accumulation, hepatic GSH but not MT mRNA levels were significantly altered in Zn-exposed fish. Cd, on the contrary, affected mainly the MT response but not GSH. Also tissue specific differences in the regulation of the two thiol pools were expressed. The thiol response after exposure to metal mixtures could not be explained by simple addition of the effects of the individual metals. The results indicate that cellular thiol pools show different reaction patterns with respect to specific metals and metal mixtures. Under conditions of long-term, low dose metal exposure, the function of GSH appears to go beyond that of a transitory, first line defense.     

Fasciola gigantica: Cercarial shedding pattern from Lymnaea natalensis after long-term exposure to cadmium at different temperatures

Little is known about the response of Fasciola spp., inside its snail host to pollutant toxicity. The effect of long-term exposure of Lymnaea natalensis to 0.1 μg/l, 10 μg/l, or 100 μg/l cadmium (Cd) on the infection rates with F. gigantica, percentage of cercariae-shedding snails and cercariae shedding pattern was investigated. The snails were exposed to Cd for 7 days either pre-infection with single Fasciola miracidium or during the late pre-patent period of the infection. The possible interaction between metal exposure and acclimatization temperature was also studied in three ranges; 16-18 °C, 23-25 °C and 30-32 °C. Results clearly showed that host exposure to 100 μg/l Cd significantly affected the pattern of Fasciola development inside its snail host, and that the acclimatization temperature was a key factor affecting the role played by Cd. Pre-infection exposure to Cd caused a significant reduction in the infection rates where the effect was temperature-dependent. Post-infection exposure to Cd significantly increased the percentage of cercariae-shedding snails; the effect was temperature-independent. Interestingly, post-infection exposure significantly altered the differential cercarial output pattern, while no clear impact on the total was found. The alteration in the differential cercarial output was represented as a significantly higher proportion of floating metacercaria as compared to fixed ones and also higher proportion of dead cercariae which may directly reduce the transmission of Fasciola to the final host. The mechanisms of cadmium impact are briefly discussed.     

Changes in selenium, zinc, copper and cadmium contents in human milk during the time when selenium has been supplemented to fertilizers in Finland

Sodium selenate has been supplemented to all agricultural fertilizers used in Finland since 1984. We followed the changes in selenium, cadmium, zinc and copper content in Finnish human milk between the years 1987 and 1993-1995. A total of 257 milk samples was collected, four weeks after delivery, in two areas: In Helsinki, an urban area, and in Kuopio, a rural area, where elevated copper concentrations have been found in the bedrock. Direct atomic absorption spectrophotometric methods without digestion were used for the analyses. The dependence of trace element content on study time, living area, smoking habits, fish eating frequency, and parity of mothers was studied by analysis of covariance. Inter-element correlations and correlations with mothers' age and fat content in milk were studied by partial correlation. Significant increases were observed in mean selenium (16.4 microg/l and 18.9 microg/l, p < 0.001) and in fat contents (3.4% and 4.0%, p < 0.001), whereas significant decreases were seen in mean zinc (3.00 mg/l and 1.47 mg/l, p < 0.001), copper (0.52 mg/l and 0.43 mg/l, p < 0.001) and cadmium contents (0.095 microg/l and 0.062 microg/l, p < 0.01). In 1987, zinc had a positive correlation with copper and fat. Copper correlated inversely with the mothers' age. In 1993-1995, selenium correlated positively with copper, and zinc correlated inversely with mothers' age. Mothers living area had an effect on copper content in milk. Our results confirm that selenium supplementation to fertilizers in Finland has increased the selenium level in human maternal milk and most likely it also has an effect on the zinc and copper concentrations in maternal milk.     

Schistosoma mansoni: production of cercarial eicosanoids as correlates of penetration and transformation

A method was developed, using a 0.25% agar matrix, to incorporate varying concentrations of linoleate and correlate cercarial transformation and eicosanoid production in vitro. Schistosoma mansoni cercariae were stimulated to penetrate over a wide range of linoleate concentrations; however, the transformation process occurred over a narrow range. Approximately 25% of cercariae penetrated the agar matrix in controls (no linoleate) and 0.003 mM linoleate. Penetration rates rose gradually until, at linoleate concentrations of 0.3 mM or greater, penetration approached 100%. The transformation process did not begin until the linoleate concentration in agar reached 2.0 mM (3.8%), and achieved maximum (91%) at 3.0 mM. A concentration of 9.0 mM linoleate gave 100% penetration and transformation rates, but penetration was superficial and cercariae were not viable. Cercarial eicosanoid production was concentration-related. Various eicosanoid classes were associated with cercarial penetration and transformation. Penetration rates were correlated with increasing leukotriene (LT, R = 0.9541) and hydroxyeicosatetraenoic acid (HETE, R = 0.8363) levels, while transformation rates correlated with increasing prostaglandin levels (R = 0.9225). Correlating eicosanoid production with penetration and transformation rates strengthened the hypothesis that successful cercarial penetration and transformation are dependent on both skin essential fatty acid levels and resulting cercarial eicosanoid production.     

Effects of copper sulphate on in vitro encystment of the cercariae of Echinostoma caproni

The effects of various concentrations of copper sulphate were studied on in vitro encystment of Echinostoma caproni in a Locke's-artificial spring water (ASW) (1:1) medium. Cercariae were killed in 10,000 mg l(-1) CuSO4 in Locke's-ASW (1:1) within 24 h and extruded cystogenous material to produce an abnormal cyst wall. The 'emergency response' of encystment to high concentrations of copper reported for Parorchis acanthus cercariae did not occur in E. caproni. Concentrations of 1000 mg l(-1) and 100 mg l(-1) CuSO4 in Locke's-ASW (1:1) also killed the cercariae without encystment by 48 h. A concentration of 10 mg l(-1) CuSO4 in Locke's-ASW (1:1) allowed for normal in vitro encystment within 48 h and these cysts were capable of excystation in a trypsin-bile salts medium.     

Effect of sub-lethal concentrations of aluminium on the filtration activity of the freshwater mussel Anodonta cygnea L. at neutral pH

Significant amounts of aluminium (Al) are commonly present in rivers and lakes, largely in particulate form in neutral waters. Freshwater bivalves, as filter feeders are therefore exposed to both particulate and dissolved metal and are potentially vulnerable to Al. The effect of Al on filtering behaviour of the freshwater mussel Anodonta cygnea L. was investigated during short (1 hour) and long-term (15 days) exposure to environmentally relevant concentrations (250 and 500 microg l(-1)) at neutral pH. Water flow through the outflow siphon was monitored as an indicator of pumping capacity. Short-term (1 hour) exposure to 500 microg l(-1) added Al produced an irreversible decrease in the duration of filtering periods, presumably as an avoidance response to the toxicant. One-hour exposure 250 microg l(-1) Al had no detectable effect. When mussels were exposed to 250 or 500 microg l(-1) added Al for 15 days, siphon activity measured in days 11-15 of exposure was inhibited by 50% and 65%, respectively, compared to pre-exposure levels. Recovery occurred following transfer of mussels to uncontaminated water. Interaction between Al and freshwater bivalves at neutral pH may affect both the performance of the mussels and the chemical speciation of the metal in the natural environment.     

Effects of zinc, copper, and selenium on placental cadmium transport

The objective of the present study was to evaluate the potential effects of zinc, copper, and selenium on placental cadmium transport. From November 2002 through January 2003, a total of 47 healthy pregnant women from Da-Ye City, Hubei Province in Central China participated in the study. Their age, parity, gestational age, pregnancy history, and lifestyle data were obtained by questionnaire interview. The placental, whole-blood, and cord blood levels of cadmium were determined by inductively coupled plasma mass spectrometer (ICP-MS), whole-blood zinc was measured by flame atomic absorption spectrometry (F-AAS), whole-blood copper by ICP-MS, and selenium was by atomic fluorescence spectrophotometry (AFS). The cord blood cadmium concentration (0.020-1.48 microg/L) was significantly lower than in maternal blood (0.80-25.20 microg/L, p<0.01). The placental cadmium concentration was from 0.082 to 3.97 microg/g dry weight. Multiple linear regression analysis indicated that lower levels of maternal blood copper were significantly associated with higher cadmium concentrations in cord blood. Placental cadmium in women with lower levels of maternal blood zinc was significantly higher than in those with normal zinc levels. The placental cadmium level in women with lower whole-blood selenium was significantly lower than in subjects with normal selenium levels. It was concluded that the essential elements copper, selenium, and zinc might significantly affect placental cadmium transport.     

The long-term effect of cadmium exposure through food on the postnatal development of the bank vole (Clethrionomys glareolus Schreber, 1780)

Cadmium is well known for its toxicity to the animal body. However, its effect on pregnancy and the development of young animals is still not well understood. This study examined such effects, using bank voles captured from the wild to make the results closer to those which could be expected in the natural environment. One group of animals was fed 7 microg g(-1) cadmium in the food, a second 35 microg g(-1), and a third no cadmium, as a control. The concentrations of cadmium in the whole bodies of young bank voles were determined on the 3rd, 5th, or 10th day of life. The cadmium level in the bodies of animals exposed to 35 microg g(-1) of cadmium was significantly higher than in those from either the control group or the group receiving 7 microg g(-1) of cadmium, which did not differ from each other. The cadmium level did not change with animal age in any of the study groups. Concentrations of Zn, Cu, and Fe were also determined in the whole body of young animals, as cadmium is known to disturb the metabolism of these essential metals through antagonistic activity. Both Cu and Fe levels were negatively correlated with cadmium concentrations, while a positive correlation was found between zinc and cadmium in the young animal bodies. Also found was higher offspring mortality in the group receiving 35 microg g(-1) of cadmium in food. There was no difference in young animal body weight between the study groups.     

Use of qPCR-Based Cercariometry to Assess Swimmer’s Itch in Recreational Lakes

Swimmer’s itch (cercarial dermatitis) is a nuisance encountered by bathers and recreational water users worldwide. The condition is caused by the penetration of larval digenean trematodes (cercariae) of the family Schistosomatidae, into the skin, following their release into freshwater from pulmonate snails that serve as the intermediate hosts for these parasites. This study utilizes qPCR-based cercariometry to monitor and quantify cercariae from water samples collected at 5 lakes in northern Michigan. The resolution provided by qPCR facilitated assessment of the environmental and biological drivers of swimmer’s itch-causing cercariae concentrations, allowing us to demonstrate that cercarial abundance is greatest at the top of the water column, in locations with prevailing on- and alongshore winds.     

Protective effect of zinc on cadmium-induced micronuclei in V79 cells

The induction of micronuclei (MN) in mitotically active cells has been widely used and promoted as a biological marker of exposure to environmental toxins. In our study the effect of zinc on cadmium genotoxicity was investigated in V 79 cells. The results indicate that cadmium chloride exposure for 24 h increased micronucleus frequency and the percentage of binucleated cells in dose-dependent manner. At the highest concentration of cadmium (50 microM Cd) 23 MN were found in 1000 cells. The protective effect of zinc on cadmium genotoxicity was investigated at lower concentrations (5-25 microM CdCl2). At 50 microM Cd, the number of MN increased significantly (16 MN).     

The effect of heavy metal accumulation on metallothionein content in selected tissues of bank voles and yellow-necked mice caught near a steelworks and zinc smelter

The effect of cadmium, zinc, and copper accumulation on metallothionein content in the selected tissues of bank voles and yellow-necked mice trapped near the Sendzimir Steelworks in Krakow and the zinc smelter in Bukowno were analysed. The Borecka Forest was chosen as a control area. The highest cadmium concentration, 32.98 microg g(-1) dry weight, was detected in the kidneys of the bank voles caught in the Bukowno area. Zinc and copper concentrations in the tissues did not exceed the critical values. Metallothionein content in the liver and kidneys was associated with heavy metal accumulation in the tissues. The highest content of sulphydryl groups was detected in the livers of the bank voles trapped within the neighbourhood of the zinc smelter in Bukowno. The highest level of disulphide bonds was found in the kidneys of the bank voles from the same area.