单独与混合暴露条件下褶纹冠蚌对Cu、Zn的积累与分布

采用室内模拟方法,在单独与混合暴露条件下研究了褶纹冠蚌(Cristaria plicata)对Cu、Zn的积累与分布特征.结果表明:褶纹冠蚌对水环境中的Cu、Zn具有良好的积累能力,持续暴露8d内,体内各组织重金属积累量基本呈线性上升,其中鳃与外套积累速率最快(p<0.05).Cu在褶纹冠蚌鳃、内脏团和生殖腺中的积累速率与Zn之间存在显著差异(p<0.05),且Cu、Zn之间在各组织中的积累拮抗作用明显.暴露前,Cu含量在褶纹冠蚌体内依次为:生殖腺>外套、内脏团>鳃、足>肌肉(p<0.05),变化幅度为10倍左右;Zn含量依次为:鳃>内脏团>生殖腺>足、外套>肌肉(p<0.05),变化幅度为4倍左右.暴露后,外套和鳃对Cu、Zn的积累量最高,且Cu、Zn含量在不同组织间的变化幅度明显增加.暴露前后,Cu含量在不同组织间的变化幅度均高于Zn.不同暴露条件下,褶纹冠蚌不同组织对Zn的浓缩系数(BCF)明显高于Cu.     

Factors affecting the accumulation and removal of mercury from tissues of the American oyster Crassostrea virginica

Adult oysters, Crassostrea virginica (Gmelin) were held in seawater containing 10 or 100 ppb mercury in the form of mercuric acetate for 45 days. Mercury concentration in tissues was determined by analysis of individually homogenized oyster meats using wet digestion and flameless absorption spectrophotometry. After 45 days, average mercury tissue concentration was 91,600 and 12,100 ppb in the 100 and 10 ppb mercury groups, respectively. A slight decline in mercury residues in the 100 ppb group during the accumulation period was attributed to spawning. Clearance of mercury from tissues was studied in a constant temperature regime (25°C±2C^o) for 25 days and in a declining temperature regime (25° to 5°C) for 80 days by exposing treated adults to estuarine water with no mercury added. The biological half-life of mercuric acetate was 16.8 and 9.3 days in the 25°C temperature regime, and 35.4 and 19.9 days in the declining temperature regime, for the 10 and 100 ppb groups, respectively. Smaller oysters (0 to 7 g) consistently accumulated more mercury per gram wet weight than larger oysters (7 to 20 g) in populations exposed to 10 and 100 ppb mercury.     

Effects of the polychlorinated biphenyl Aroclor® 1254 on the American oyster Crassostrea virginica

Young oysters (Crassostrea virginica) were continuously exposed to Aroclor^® 1254, a polychlorinated biphenyl (PCB), in flowing, unfiltered seawater. Growth rate (height and in-water weight) was significantly reduced (=0.05) in oysters exposed to 5 g/l (ppb) for 24 weeks. Growth rate was not affected in oysters exposed to 1 ppb for 30 weeks. Mortality was not significant in exposed and control groups. In oysters exposed to 5 ppb, greatest PCB residue (whole body) was 425 mg/kg (ppm), 85,000x the concentration in the water, and less than 0.3 ppm was retained after 28 weeks depuration in PCB-free water. In oysters exposed to 1 ppb, greatest residue was 101 ppm, 101,000x the concentration in the water, and less than 0.2 ppm was retained after 12 weeks depuration. Examination of oysters exposed to 5 ppb of this PCB for pathogenesis revealed atrophy of digestive diverticular epithelium and degeneration of vesicular connective tissues concomitant with leukocytic infiltration, but tissue recovery seemed excellent after 12 weeks depuration.Registered trademark, Monsanto Company, St. Louis, Missouri, USA. Mention of commercial products or trade names does not constitute endorsement by the Environmental Protection Agency.Contribution No. 146, Gulf Breeze Laboratory.     

Depuration of twelve trace metals in tissues of the oysters Crassostrea gigas and C. virginica

The depuration of 12 trace metals in the mantle, gill, digestive gland, and kidney of Crassostrea gigas and C. virginica was investigated under natural field conditions; oysters from a relatively contaminated environment (Redwood Creek in south San Francisco Bay) were transplanted to a relatively clean environment (Tomales Bay). In the transplanted oysters, the digestive gland and kidney depurated Cd, Cu, Hg, Ag, and Zn more readily than the mantle and gill. Other trace metals As, Fe, Mn, Ni and Se showed varying depuration patterns. The results for Cr and Pb were inconclusive, since initial concentrations were too low to follow any losses. Interspecific differences in trace metal depuration were observed. Biological half-lives for most trace metals were on the order of 23 to 60 d for C. gigas and on the order of 70 to 180 d for C. virginica.     

Role of adipocytes in the muscle tissue of Atlantic salmon (Salmo salar ) in the uptake, release and retention of water-soluble fraction of crude oil hydrocarbons

The uptake and depuration of the water-sol‐uble fraction (WSF) of hydrocarbons of crude petroleum by Atlantic salmon (Salmosalar) has previously been examined in terms of whole muscle. The hypothesis that the tainting WSF in the muscle was retained primarily by adipocytes has been investigated by the isolation of adipocytes and the subsequent analysis for hydrocarbons in adipocytes. After 96 h exposure of market-sized Atlantic salmon to 0.2 ppm WSF, adipocytes isolated from the belly flap region of the muscle tissue accumulated 14.3 times more WSF (59.4 ppm) than the dorsal white muscle (4.2 ppm), while 54% of the tainting WSF in the dorsal white muscle was found to be stored in associated adipocytes. When returned to clean seawater, WSF accumulated in the dorsal white muscle was released much faster than that in the adipocytes. These results indicated that the loose association of WSF with the nonlipid portion of white muscle, mainly muscle cells and intercellular fluid, is responsible for the rapid discharge of WSF from the dorsal muscle tissue in the early stages of depuration. After 4 d of depuration, the adipocytes became the principal storage site of residual WSF in white muscle and the depuration of WSF from muscle tissue then reflected the release of WSF from adipocytes in the muscle tissue. After 20 d of depuration, 10.7 ppm of tainting WSF in the form of high molecular weight aromatic hydrocarbons (mainly C₄-benzenes, naphthalene and alkylated naphthalenes) were still present in adipocytes, while in the dorsal white muscle only a trace of total WSF was detected. Increases in the number of aromatic rings and the alkylations on the rings enhanced the accumulation and retention of individual hydrocarbons in both adipocytes and white muscle. From these studies we conclude that it is the adipocytes in the muscle tissue which control the actual accumulation and release of hydrocarbons in the whole muscle tissue of Atlantic salmon. Received: 21 August 1996 / Accepted: 26 September 1996     

Effects of arsenic on osmoregulation in the tilapia Oreochromis mossambicus reared in seawater

The effects of arsenic (As₂O₃) on plasma osmolarity, Na and K concentrations, the activity of gill Na–K-ATPase, and on the ultrastructure of gill chloride cells were compared between seawater tilapia (Oreochromis mossambicus) and freshwater tilapia in the Institute of Zoology, Academia Sinica, between 1989 and 1991. Arsenic was found to be more lethal in seawater tilapia [96 h LC₅₀ (median lethal concentration): 26.5 ppm] than in freshwater ones (71.7 ppm). No significant effect was found on plasma ion concentrations and osmolarity, enzyme activity or the ultrastructure of chloride cells in freshwater tilapia after 96 h exposure to 70 ppm arsenic. In contrast, 96 h exposure to 15 ppm arsenic caused evident effects in seawater tilapia: an increase in plasma osmolarity and activity of gill Na–K-ATPase, as well as better development of the chloride cell tubular system. These data suggest that the lethal effect of arsenic may be partially attributed to a hydromineral disturbance in seawater tilapia, but in freshwater tilapia arsenic perhaps causes destruction in some physiological mechanisms other than osmoregulation. The activation of gill Na–K-ATPase and chloride cells in seawater tilapia appears to indicate an adaptation in the osmoregulatory mechanism to arsenic exposure, i.e., to enhance secreting ions or arsenic in the gills.     

镉在方斑东风螺组织内的蓄积及镉的毒性：水相暴露与食物相暴露比较

为比较直接经水体与经营养传递的2种镉(cadmium,Cd)暴露方式对方斑东风螺(Babylonia areolata)不同组织Cd蓄积和毒性的差异,采用室内模拟法,将螺暴露于含Cd水体(Cd2+:100μg·L-1)或喂食含Cd饵料(牡蛎,34.56μg·g-1以干质量计,先经水体100μg·L-1Cd2+暴露达平衡)30d后再进行15d净化。结果显示,暴露期间,除食物相组螺胃肠道Cd浓度在第10天极显著高于对照组,但随后迅速下降外,其他各组织在2种途径及胃肠道在水相暴露时Cd的浓度均逐渐上升,暴露30d后肝胰脏中Cd浓度最高;净化期,螺鳃中Cd排出率较高,胃肠道与肝胰脏的排出率较低,至净化期末除食物相组鳃中Cd浓度与对照组无显著差异外,2种处理中其他各组织Cd浓度仍显著高于对照组。2种暴露途径中金属硫蛋白(metallothionein,MT)浓度仅在螺肝胰脏中逐渐增加,且与Cd的蓄积呈显著线性正相关。与食物相组相比,水相Cd暴露引起螺肝胰脏脂质过氧化水平(lipid peroxidation,LPO)更高,且内脏团中Cd与其亚细胞成分的金属敏感组分结合的百分比也更高。结果表明,Cd通过营养传递对螺产生的毒性较水体直接暴露低,但摄食是螺蓄积Cd的主要途径;净化后除鳃外水相暴露组螺各组织Cd的排出率较低;因此为了健康养殖与食用安全,东风螺工厂化养成时对饵料与水体Cd浓度的监测均应引起足够的重视。     

Characterisation and expression of four mRNA sequences encoding glutathione S-transferases pi,mu, omega and sigma classes in the Pacific oyster<Emphasis Type="Italic"> Crassostrea gigas</Emphasis> exposed to hydrocarbons and pesticides

Hydrocarbon and pesticide pollution in coastal ecosystems can disturb marine bivalve metabolism. In this study, we characterised four full-length cDNA sequences encoding glutathione S-transferases (GSTs) in the Pacific oyster Crassostrea gigas. A BLAST X search showed that these four sequences encode GSTs from four different classes: GST pi, sigma, mu and omega. A phylogenetic analysis of GST was made to determine the position of oyster GST compared to invertebrate and vertebrate sequences. We developed a semi-quantitative, multiplex RT-PCR to follow the expression of these four GSTs in tissues of oysters exposed to hydrocarbons and two pesticide treatments (glyphosate and a mixture composed of atrazine, diuron and isoproturon) under experimental conditions. Our results showed strong differential expression of these four GSTs that was both tissue specific as well as time and treatment dependent. We observed that expression levels were higher in digestive gland than in gill tissues in pesticide-exposed oysters. Furthermore, omega and mu class GST mRNA expression in the digestive gland might be useful as a possible marker of hydrocarbon exposure, while pi and sigma class GST mRNA expression in the digestive gland may be similarly useful as a marker of pesticide exposure in monitoring programmes.Communicated by S.A. Poulet, Roscoff     

Accumulation and depuration of mercury in the American oyster Crassostrea virginica

To study the kinetics of mercury uptake in oysters, adult Crassostrea virginica (Gmelin) were held in seawater containing 10 g mercury/l (ppb) or 100 g mercury/l (ppb), added in the form of mercuric acetate, for 60 days. Mercury concentration in tissues was determined by analysis of individually homogenized oyster meats, using wet digestion and flameless absorption spectrophotometry. After 45 days, average mercury tissue concentration was 140,000 g mercury/kg tissue (ppb) and 28,000 g mercury/kg tissue (ppb) in the 100 ppb and 10 ppb experimental groups, respectively. After this time, concentrations dropped sharply, probably due to spawning. Clearance of mercury from tissue was studied by exposing treated adults to estuarine water (with no additions) for 30 days (100 ppb group) and 160 days (10 ppb group). Tissue concentrations in the 100 ppb mercury environment group declined from 115,000 to 65,000 ppb, and those of the 10 ppb group declined from 18,000 to 15,000 ppb, in 18 days; there-after, no further decline occurred in either group. Oysters accumulated mercury 1,400 times and 2,800 times above the environmental concentrations of 100 and 10 ppb mercury, respectively. Total self-purification was not achieved over a 6 month cleansing period.     

Combined effect of the chlorides of mercury and copper in sea water on the euryhaline amphipod Gammarus duebeni

The possible interactive effect of the chlorides of copper and mercury on the euryhaline amphipod Gammarus duebeni in 100% sea water was examined using the following indices: (i) 96 h LC50 values, (ii) urine production rates and (iii) degree of mercury accumulation. Both (a) the interaction of the chlorides of mercury and copper together in solution and (b) the influence of cupric chloride pre-treatment of individuals prior to exposure to mercuric chloride were investigated. Presence of a sublethal level of cupric chloride protected G. duebeni against the toxic action of mercuric chloride. Cupric chloride pretreatment was not so effective. The nature of the interaction between mercury and copper is discussed.     

Lead- and cadmium-induced histopathological changes in gill,kidney and liver tissue of freshwater climbing perch Anabas testudineus (Bloch, 1792)

The objective of this study was to examine the toxicological effect of two major heavy metal pollutants, lead chloride (PbCl₂) and cadmium chloride (CdCl₂), in the freshwater climbing perch, Anabas testudineus. Fish were exposed to 1.0 and 2.0 mg/L both metals and histopathological changes in gill, kidney and liver tissues were studied. Major changes observed in gill tissue were epithelial lifting, proliferation of epithelial cells, fusion of secondary lamellae, hyperplasia and hypertrophy of mucous cells, and necrosis of epithelial cells. Cell necrosis, degenerated kidney tubules, congestion, lymphocytic infiltration and vacuolation were the major abnormalities observed in kidney tissue. The most conspicuous changes in liver were darker nucleoli, irregularly shaped hepatocytes with dilated blood capillaries, and focal as well as single necrosis. Fish specimens exposed to PbCl₂ exhibited pronounced changes in all tissues examined compared with those exposed to CdCl₂. It is evident from this study that heavy metals can cause significant histopathological changes in fish tissue.     

Mercury induced architectural alterations in the gill surface of a fresh water fish,Channa punctatus

An air-breathing fresh waterfish Channa punctatus was exposed chronically to sublethal concentrations of mercuric chloride and the respiratory surface was found to exhibit lesions, lifting of lamellar epithelium and increased number of mucus gland openings. The damage increased with increase in the concentrations. The gill surface was studied using scanning electron microscope.     

饲料中铜暴露对吉富罗非鱼幼鱼血红细胞微核和组织中铜蓄积的影响

为了研究饲料中铜暴露对吉富罗非鱼幼鱼的毒性作用,将1 080条罗非鱼幼鱼暴露于6个浓度梯度的高铜日粮中,通过60 d的暴露试验,测定罗非鱼血红细胞微核变化和组织中铜的蓄积.结果表明,铜在各组织中积累量的顺序依次为:肝脏＞脾脏＞肠道＞鳃＞肌肉,与对照组相比,其中肝脏、脾脏、肠道中铜的含量随着时间和日粮中铜浓度的升高而逐渐升高,而鳃和肌肉中铜含量无显著差异;罗非鱼幼鱼血红细胞微核率、核异常率、总核异常率与日粮中铜的浓度存在一定的剂量—效应关系,并且核异常率高于微核率.     

Field depuration and biotransformation of paralytic shellfish toxins in scallop<Emphasis Type="Italic"> Chlamys nobilis</Emphasis> and green-lipped mussel<Emphasis Type="Italic"> Perna viridis</Emphasis>

Under laboratory conditions, the scallop Chlamys nobilis and the mussel Perna viridis were exposed to N-sulfocarbamoyl toxins (C2 toxin), a paralytic shellfish toxin (PST), by feeding a local toxic strain of the dinoflagellate Alexandrium tamarense (ATDP) that produced C2 toxin exclusively. The bivalves were subsequently depurated in the field, and their depuration kinetics, biotransformation and toxin distribution were quantified. Depuration was characterized by a rapid loss within the first day, followed by a secondary slower loss of toxins. In the fast depuration phase, scallops detoxified PSTs more quickly than the mussels (depuration rate constants for scallops and mussels were 1.16 day^–1 and 0.87 day^–1, respectively). In contrast, the mussels detoxified PSTs more quickly than the scallops in the slow depuration phase, and the calculated depuration rate constants (mean+SE) from day 2 to day 13 were 0.063+0.009 day^–1 and 0.040+0.019 day^–1 for mussels and scallops, respectively. The differences in the appearances of gonyautoxins, GTX2 and GTX3, and their decarbamoyl derivatives, dcGTX2, dcGTX3 and GTX5, which are all derivatives of C2 toxin, indicated active and species-specific biotransformation of the algal toxins in the two bivalves. In both species of bivalves, the non-viscera tissue contained fewer toxins and lower concentrations than the viscera-containing tissue compartment. In scallops, very little toxin was distributed in the adductor muscle. In mussels, most of the PSTs were found in the digestive gland with significant transport of toxins into the digestive gland from other tissues during the course of depuration. The toxin profiles of scallops and mussels differed from each other and from that of the toxic algae fed. A significant fraction of GTX5 was detected in the mussels but not in the scallops. Our study demonstrates a species specificity in the depuration kinetics, biotransformation and tissue distribution of PSTs among different bivalves.Communicated by T. Ikeda, Hakodate     

纳米氧化镍颗粒对长牡蛎(Crassostreagigas)抗氧化防御体系的影响

纳米氧化镍(nNiO)作为一种广泛使用的纳米颗粒,其水生毒理效应研究还很有限。为探索n Ni O对海洋贝类的毒性机制,本研究将长牡蛎(Crassostrea gigas)置于不同浓度(0、1、10、100 mg·L~(-1))的n Ni O中暴露96 h,分别测定鳃和消化腺组织的丙二醛(MDA)含量和超氧化物歧化酶(SOD)、过氧化物酶(POD)以及过氧化氢酶(CAT)活性,并通过实时荧光定量PCR技术测定了鳃和消化腺中应激蛋白HSP70和AOX基因的表达变化。结果显示:在100 mg·L~(-1)n Ni O处理下,2种组织中MDA含量均显著性升高(P0.01),显示纳米颗粒造成了长牡蛎的脂质过氧化,并可能引起相应的氧化损伤。同时,n Ni O暴露也诱导了长牡蛎抗氧化酶(SOD、CAT和POD)活性的改变。其中,SOD和CAT活性在10 mg·L~(-1)浓度处理组达到最高,而POD活性在1 mg·L~(-1)浓度组即达最高值。在高浓度n Ni O(100 mg·L~(-1))胁迫下,3种抗氧化酶的活性均比低浓度(1和10 mg·L~(-1))处理组降低,表明抗氧化酶的保护作用在较低浓度暴露下更有效;而热激蛋白(hsp70)和交替氧化酶(aox)基因却分别在长牡蛎消化腺和鳃组织中上调表达(P0.01),并表现出一定的组织差异。说明高浓度纳米颗粒暴露中主要是应激蛋白发挥了作用。本文结果为纳米氧化镍对海洋双壳贝类的毒性机制研究及生态风险评估提供了基础数据。     

Survival and chloride ion regulation of the porcelain crab Petrolisthes armatus exposed to mercury

Acute toxicity bioassays conducted at various salinities demonstrated that mercury (as mercuric chloride) at low concentrations was lethal to Petrolisthes armatus. Ninety-six hour LC₅₀ values varied from 50 to 64 parts per billion (ppb) of mercury, depending on test salinities. Lower salinities. decreased the time to death of mercuryexposed crabs. Differences in survival after 96 h due to salinity were not statistically significant. Blood chloride concentrations were regulated hyperchloride to the medium at low salinities and hypochloride at high salinities by acclimated crabs. The salinity isochloride to blood was 20 S. Transfer of crabs from 15 S to salinities ranging from 7 to 35 S resulted in new steadystate chloride levels within 12 h. Exposure to 50 ppb mercury did not alter chloride ion regulation of either acclimated crabs or crabs adjusting to new salinities.     

Influence of temperature and salinity on the uptake,distribution and depuration of mercury,cadmium and lead by the black-lip oyster Saccostrea echinata

Saccostrea echinata (Quoy and Gaimard) were exposed to 10 g 1^-1 of either mercury, cadmium or lead at 30 °C, 36S; 30 °C, 20S; 20°C, 36S and 20°C, 20S for 30 d and were then transferred to clean seawater for a further 30 d to depurate. Specimens were removed at regular intervals during the exposure and depuration periods, dissected into gills, mantle, visceral mass and adductor, and analysed for the appropriate metal by atomic absorption spectroscopy. Mercury was concentrated more than the other metals in all tissues under all conditions. Cadmium uptake was greater than lead in all tissue in the high-temperature experiments, whereas both metals were concentrated to similar extents at low temperature. The gill tissue generally accumulated the greatest amount of all 3 metals, whilst the adductor concentrated the least amount. At both salinities, mercury and cadmium accumulation by all tissues was significantly greater at the higher temperature whereas lead uptake was only marginally increased. The accumulation rates of mercury at high temperature were significantly greater in all tissues at low compared with high salinity, whereas at low temperature, differences were not significant. Accumulation rates of cadmium and lead in the majority of tissues examined were significantly greater in lowsalinity water at both temperatures. In general, lead was lost the most rapidly from oyster tissues, followed by mercury and then cadmium. The residence times for mercury and cadmium differed significantly between tissues, with the gills showing the highest turnover rate. In contrast, residence times for lead were similar between tissues. Losses of all 3 metals from oyster tissues were not obviously influenced by temperature and only mercury losses differed significantly between salinities.     

Extra- and intracellular acid-base balance and ionic regulation in cod (Gadus morhua ) during combined and isolated exposures to hypercapnia and copper

Cod (Gadus morhua) were exposed to hypercapnia (water Pco₂ = 7.5 mmHg), elevated copper level (0.4 ppm) or a combination of both in order to study extra- and intracellular acid-base regulation and the influence hereupon of copper. During pure hypercapnia, the extracellular respiratory acidosis was completely compensated within 12 to 24 h via a chloride-mediated increase in extracellular [HCO₃ ⁻]. Exposure to copper in normocapnic seawater caused a large and progressive increase in plasma [Na⁺] and [Cl⁻] and a metabolic acidosis. Exposure to copper in hypercapnic seawater was associated with smaller elevations of plasma [Na⁺] and [Cl⁻] than in normocapnic seawater, showing that hypercapnia had a protective effect on the copper-induced osmoregulatory disturbances. The compensation of the hypercapnic acidosis was, however, slow and incomplete in fish exposed to both copper and hypercapnia. Extracellular pH remained depressed by 0.3 pH units after 72 h. The data reveal that acid-base regulation was immediately and persistently inhibited by copper. The limited acid-base regulation during combined copper and hypercapnia exposure was chloride-mediated as during hypercapnia alone. Intracellular pH recovery was complete and very rapid in ventricular and skeletal muscle tissues during environmental hypercapnia, whereas acid-base compensation in liver tissue was slower, the kinetics being similar to that in the extracellular compartment. Intracellular pH compensation was significantly slowed down by copper. Copper concentration increased drastically in gill tissue already at 3 h, while copper concentrations in liver, muscle and plasma were significantly elevated only after 48 h, with liver showing the largest elevation. Received: 15 November 1996 / Accepted: 2 December 1996     

Fluxes of dissolved and particulate calcium in selected tissues of Crassostrea virginica

Rates of calcium incorporation by selected tissues of Crassostrea virginica increased in a step-wise fashion from lowest values among organisms exposed to ambient total calcium concentrations of 45 mg l^-1, intermediate values among oysters exposed to 135, 225, and 315 mg l^-1, to highest rates for oysters exposed to 360 mg l^-1. Although excised visceral mass tissue had highest rates of calcium incorporation relative to mantle, muscle, and both organic and inorganic portions of the shell, mantle tissue appeared to have the most dynamic response to changes in ambient calcium concentrations. Rates of dissolved calcium incorporation from ambient water were approximately two to three orders of magnitude higher than comparable rates from ingested algal food. Behavioral response to concentrations of selected inoic, species in the ambient environment may have been responsible for observed differences in rates of calcium incorporation.     

Histochemical demonstration of mercury in the intestine,nephridia and epidermis of the marine polychaete Nereis virens exposed to inorganic mercury

Marine polychaetes Nereis virens (Sars) were exposed to 9 ppb Hg as mercuric chloride in the aquarium water. Concentrations of mercury in the water and in the worms were monitored using radiolabelled mercury. After 11 d, the average mercury concentration in the nereids was 8.41 ppm Hg and the bioconcentration factor was calculated to be 930. Accumulations of mercury in the tissues were made visible for light and electron microscopy by autometallographic silver enhancement. Mercury was demonstrated in the intestine, nephridia, epidermis and cuticula. In the intestine, mercury was found to be located predominantly in the apical part of the epithelial cells. In the nephridia, mercury deposits were apparent in the peritoneal cells of the nephridial tubules. Silver-enhanced mercury was also observed at the epicuticula, in the collagen fibres of the endocuticula and in the epidermal basal cells. Intracellularly, the observed mercury accumulations were localised predominantly in lysosomes. Extracellularly, mercury was observed in the basal laminae of the intestine and the epidermis, and also in the intestinal peritrophic membrane. How N. virens copes with mercury toxicity is discussed.