Comparative toxicity of drilling muds: role of chromium and petroleum hydrocarbons

Samples of used drilling muds collected during the course of a single well drilling operation exhibited different degrees of acute toxicity to sheepshead minnows and grass shrimp. For moulting grass shrimp, Palaemonetes pugio, the 96-h LC₅₀'s were 360 to 14 560 ppm (μl/litre); many of these values were considerably lower than those reported from previous drilling mud assays. However, when some of the muds used in this study were tested on sheepshead minnows, Cyprinodon variegatus, the resulting 96-h LC₅₀'s (6300 to 100 000ppm) were well within the range of previously reported values.Although a number of the drilling mud samples had relatively high amounts of chromium due to the addition of sodium chromate, there was a low correlation between chromium concentration and toxicity. In only three drilling muds could chromium content alone account for the observed toxicities. Furthermore, chemical analyses revealed the presence of No. 2 fuel oil like petroleum hydrocarbons in the mud samples. Based on the results of toxicity tests with No. 2 fuel oil and the concentrations of oil present in the muds, the toxicity of the mud samples to grass shrimp appears to be largely attributable to the petroleum hydrocarbon content.     

Acute toxicity of bromochlorinated seawater to selected estuarine species with a comparison to chlorinated seawater toxicity

The acute toxicity of bromochlorinated estuarine water (ca. 20%) was determined for several estuarine organisms. The most sensitive species were oysters (Crassostrea virginica, larvae and juveniles) and copepods (Acartia tonsa) with 48-h LC₅₀'s of 0·10 to 0·21 mg BrCl/litre. Palaemonetes pugio was most tolerant with a 96-h LC₅₀ of 0·70 mg BrCl/litre. The fish species tested (Menidia menidia, Brevoortia tyrannus and Leiostomus xanthurus) all had a 96-h LC₅₀ of 0·21–0·23 mg BrCl/litre.The BrCl toxicity data are compared with Cl₂ toxicity data for the same species. When the LC₅₀'s are expressed as equivalents per litre, BrCl is found to be two to four times less toxic than Cl₂. The ranking of species in terms of sensitivity is the same for both disinfectants.Some data are provided concerning the decay rates of BrCl and Cl₂ in estuarine water. BrCl was found to decay more rapidly than Cl₂ at higher ammonia levels (0·25 mg NH₄-N/litre). The question of chemical speciation is discussed with particular reference to the differential toxicities.     

Toxic effects of certain heavy metals (Hg,Cd, Pb,As and Se) on the intertidal crab scylla serrata

The toxic effects of certain heavy metals (Hg, Cd, Se, As and Pb) on Scylla serrata, the common edible Indian marine crab, are evaluated. Mercuric chloride, phenyl mercuric acetate (PMA), cadmium chloride, selenium dioxide, arsenic trioxide and lead nitrate were tested individually in laboratory static bioassays using artificial seawater to determine the 24 to 96 h LC₅₀ values. As indicated by 96 h LC₅₀ values PMA was found to be the most toxic and lead nitrate the least toxic. CdCl₂ showed a 6·6 fold increase in toxicity with increase in the time of exposure from 24 to 96 h. Marked histopathological changes were noticed in the hepatopancreas and gill of Scylla serrata exposed to acute 96 h LC₅₀ values of these metal compounds. 30 days' long-term exposure to sublethal concentrations of mercury and cadmium brought about degenerative changes in the hepatopancreas and gill of exposed animals. Extensive cellular proliferation (hyperplasia) of secondary lamellae accompanied by cyst formation and necrotic regions were often seen in the gills of cadmium treated crabs. Interestingly enough, the free amino acid pool from muscle and hepatopancreas of treated animals, either after acute or long-term exposure, did not show any reduction in number or quantity     

Disruption of magnesium regulation in the crab Cancer productus exposed to chlorinated seawater

Exposure of the crab Cancer productus to chlorinated seawater resulted in alterations in haemolymph sodium and magnesium concentrations. At the highest chlorination levels, which approached the 96-h LC₅₀, regulation of both ions was essentially abolished. Reciprocal changes in the sodium and magnesium levels suggested an effect on the activity of the bladder wall, which has been implicated in the regulation of haemolymph magnesium in crustaceans.Additionally, exposure to 1·19 μg/ml applied Cl (0·68 μg/ml TRO) for 96 h resulted in a fourfold increase in the ammonia excretion rate. Crabs also contributed considerable chlorine demand to the exposure seawater. Measurements of TRO in the inhalant seawater and water exiting the crabs' branchial chambers indicated a reduction in TRO equivalent to 57% of that initially present in the inhalant water (0·51 μg/ml TRO).Measurements of ammonia concentrations in the exposure water indicated that ammonia in seawater was consumed in reactions with oxidants. This was especially evident at higher levels of chlorination. At 0·58 μg/ml applied Cl and above, chlorination resulted in near disappearance of ammonia from the water.     

Behavioural responses of selected marine fishes to chlorinated seawater

Behavioural responses to chlorinated seawater were studied in the laboratory using eight species of fish (topsmelt, Atherinops affinis [Ayres]; pile perch, Rhacochilus vacca [Girard]; señorita, Oxyjulis californica [Günther]; blacksmith, Chromis punctipinnis [Cooper]; northern anchovy, Engraulis mordax [Girard]; opaleye, Girella nigricans [Ayres]; bluebanded goby, Lythrypnus dalli [Gilbert] and mussel blenny, Hypsoblennius jenkinsi Jordan and Evermann) which occur near the Units 7 and 8 discharge of Southern California Edison's Redondo Beach Steam Generating Plant in King Harbor, California, USA. All species except Engraulis demonstrated prolonged avoidance of chlorinated quadrants of the behaviour chamber. The avoidance thresholds were species-specific and species totally avoided estimated total residual oxidant (TRO) concentrations from 0·094 to 0·456 mg/litre. Calculated significant avoidance thresholds averaged 0·066 mg/litre TRO; young Atherinops significantly avoided TRO concentrations as low as 0·028 mg/litre (p < 0·001). The highest avoidance thresholds were exhibited by sedentary species and were modified by the presence of cover inside the behaviour chamber. The avoidance response protected against mortality in all species except Lythrypnus and Engraulis.     

Evidence on the interaction of mercury and selenium in the shrimp Palaemon elegans

The interaction of selenium with mercury was studied in the shrimp Palaemon elegans. The release of ²⁰³HgCl₂ (5·0 μg Hg per gramme body weight) from shrimp pretreated with selenium (SeO₂ doses of 1·97, 3·95 and 7·90 μg Se per gramme fresh weight) was significantly decreased compared with the control group to which only 5·0 μg Hg/g had been administered.In the presence of HgCl₂ (5·0 μg Hg per gramme fresh weight) the release of ⁷⁵Se also diminished significantly at the higher stable Se pretreated dose (7·90 μg Se/g) while, at a lower selenium concentration, the release was not statistically different. Analyses for stable Hg and Se confirmed the decrease in rate of selenium loss in the presence of mercury which had been demonstrated with radiotracers.A dose of 7·9 μg Se per gramme fresh weight injected 12 h before exposure of the shrimp to the various mercuric chloride solutions did not produce a significant difference in the 24 h LC₅₀ compared with the group not pretreated with selenium. However, during exposure to mercury at 3·8 mg/litre, the median lethal time (LT₅₀) for the shrimp pretreated for 4 days with sublethal selenium (6·9 and 10·5 mg Se/litre) was delayed (19·2 and 33·2 h) compared with the group which was not pretreated. The results are discussed in relation to the role of selenium in the acutely toxic effects of inorganic mercury.     

A comparison of ozone and chlorine toxicity to three life stages of the American oyster Crassostrea virginica

The effects of ozone-produced oxidants (OPO) on three developmental stages of the American oyster, Crassostrea virginica, were evaluated. Both straight-hinge (48-h post fertilisation) and setting pediveliger larvae were exposed to a series of OPO concentrations ranging from 0·05 to 0·30 mg/litre OPO (as total residual chlorine) at 25°C for 96 h. Mortality was used as the response parameter and results were quantitatively compared with the effects of chlorine-produced oxidants (CPO) obtained from the literature on these same developmental stages. Adult oysters (2- to 4-year class) were exposed to OPO concentrations ranging from 0·01 to 0·50 mg/litre at 15°C for 5 days and to the same concentration range at 25°C for two consecutive 6-day periods. Shell deposition and faecal matter accumulation were used as the response parameters for this stage.Straight-hinge larvae were significantly more sensitive to OPO than setting pediveliger larvae. Both larval stages were significantly more sensitive to CPO than to OPO. Shell deposition was significantly inhibited at all OPO concentrations for both 15°C and 25°C acclimated adult oysters. No significant differences were found between the shell deposition response of oysters at the two acclimation temperatures. Faecal matter accumulation was significantly reduced at OPO concentrations ≥ 0·05 mg/litre at both 15°C and 25°C. It was significantly (p < 0·05) greater for 25°C acclimated oysters than for 15°C acclimated oysters at OPO concentrations < 0·10 mg/litre but not at higher concentrations.     

Cadmium acclimation and limb regeneration in the fiddler crab, Uca pugilator: Sex differences

After multiple autotomy in the fiddler crab, Uca pugilator, cadmium retards limb regeneration and ecdysis. To study the effects of pre-exposure to lower levels of cadmium, groups were pre-exposed to 0·1, 0·5 or 1·0 mg liter^?1 for a week prior to autotomy. Crabs were then placed in 1·0 mg liter^?1 for regeneration. Pre-exposed groups were compared with groups of crabs which had not been pre-exposed to Cd. It was found that males pre-exposed to 0·5 mg liter^?1 regenerated more rapidly in 1·0 mg liter^?1 than those not pre-exposed. This phenomenon was not observed in females, in which none of the three pre-exposure concentrations were able to accelerate regeneration in 1·0 mg liter^?1 relative to those not pre-exposed. In the pre-exposed males in which regeneration was accelerated and was comparable to control levels, no accompanying decrease of time until molting was observed. Therefore, the protective effect of pre-exposure would seem to be on the regeneration processes themselves and is not dependent on the neuroendocrine system which controls the molt cycle.     

Detection of the water-soluble fraction of crude oil by the blue crab, Callinectes sapidus

The ability of the blue crab, Callinectes sapidus, to detect petroleum hydrocarbons was measured with behavioural techniques. When presented with a water-soluble fraction of Prudhoe Bay crude oil, blue crabs abruptly changed antennular orientation, began rhythmic beating of the maxillipedal flagellae, and increased antennular flicking rate. The threshold concentration at which 50% of the crabs detected the water-soluble fraction was 2 × 10^?6 mg/litre. The blue crab apparently can readily detect petroleum hydrocarbons at concentrations found in chronically polluted areas as well as oil spill situations.     

The uptake and accumulation of Ni by Cerastoderma edule and its effect on mortality,body condition and respiration rate

The concentration of Ni in C. edule ranges from 17·8 μg/g to 53·82 μg/g with the highest concentration in the gills and mantle and the lowest in the foot and adductor muscles. The concentration does not change with either size or season.There is no significant increase in mortality even in the highest Ni concentration (100 μg/litre), nor is body condition correlated with experimental Ni concentrations. The rate of uptake of Ni (y) is described by the equation:

$\text{y=?16·903+11·674x}{}_1\text{+0·437x}{}_2$

where x₁ = Ni concentration (μg/litre) and x₂ = time (h).The respiration rates did not significantly change up to the highest Ni concentration used (1000 μg/litre).It is postulated that the main pathway for Ni uptake is through the gills, possibly through mucus sheet or transmembrane absorption, with a secondary uptake route via the viscera.C. edule may therefore be a suitable indicator species for Ni.     

Oxygen consumption in the shrimp,Palaemonetes pugio,exposed to fluctuating temperatures and food contaminated with the diaromatic petroleum hydrocarbon,dimethylnaphthalene

Oxygen consumption rates (V?o₂) in the grass shrimp Palaemonetes pugio were determined after a 32 day exposure to fluctuating temperatures (FT) (18–22°C) and/or dimethylnaphthalene (DMN)-contaminated food (0·24 μg DMN g wet wt^?1) and again after a 16 day recovery period of stable temperatures (20°C) and uncontaminated food. Ingestion of DMN-contaminated food for 32 days resulted in elevated V?>o₂ in shrimp exposed to declining oxygen concentrations. After the 32 day exposure period, FT had no significant effect on V?o₂ at 15, 20 and 25°C, tissue V?o₂ and V?o₂ in declining oxygen. Hemolymph copper concentrations were significantly depressed in shrimp exposed to DMN-contaminated food. After the 16 day recovery period, shrimp from the FT regime exhibited depressed V?o₂ when exposed to 25°C but not to 15°C. These depressed respiratory rates were offset by the stimulatory effect of DMN-contaminated food.These respiration studies were generally unproductive in explaining the previously reported effects of FT and DMN-contaminated food on the survival of P. pugio under hypoxic conditions.     

Toxic contributions of specific drilling mud components to larval shrimp and crabs

We investigated the toxicities of six drilling muds, toxicities of mud fractions (supernatants and suspensions) and the toxicities of common mud components—barite and bentonite (particulates) and ferrochrome lignosulfonate (soluble)—to the stage I larvae of six species of shrimp and crab. The drilling muds we tested were not very toxic to these larvae: LC₅₀'s for supernatants ranged from 0·6 to 82% (vol/vol). Shrimp larvae were slightly more sensitive than crab larvae.Drilling muds were not rapidly toxic, in contrast to toxicants such as the water-soluble fractions of oil. Supernatants, prepared by centrifuging whole muds, were mildly toxic. Suspensions were more toxic than supernatants and toxicity was greatest when particulates remained suspended: for example, used Cook Inlet mud suspensions were about seven times more toxic than supernatants. The toxicity of used Cook Inlet mud was therefore primarily due to suspended solids (88%) rather than chemical toxicity: ferrochrome lignosulfonate was relatively toxic alone, but accounted for only about 6% of the toxicity of used Cook Inlet mud suspensions. Contributions of particulates to mud toxicities varied considerably. Barite and bentonite were not very toxic when tested alone. The toxicity of one mud was caused by its high alkalinity.     

Toxicity of copper to three estuarine bivalves

This paper reports on a study of the toxicity of copper to three species of bivalve of commercial food value, Anadara granosa (Linnaeus), Meretrix casta, Deshayes and Crassostrea madrasensis (Preston) inhibiting the Vellar estuary at Porto Novo (southern India). The LC₅₀ values were estimated as 60 μg Cu/litre for A. granosa, 72 μg Cu/litre for M. casta and 88 μg Cu/litre for C. madrasensis subjected to 96-h static bioassay tests after acclimation for a period of four days in the laboratory. The animals selected for study ranged in length from 29 to 44 mm in A. granosa, from 25 to 42 mm in M. casta and from 31 to 115 mm in C. madrasensis. The experiments were conducted at 25% salinity with pH 8·0 ± 0·1 at a temperature of 27°C ± 0·5°C. The revival rates of bivalves which survived exposure to the LC₅₀ concentrations for the 96-h period (when marked and released in the natural environment) were 67% for A. granosa, and C. madrasensis and 83% for M. casta. The LT₅₀ values for the three bivalves at different concentrations of the metal were also calculated.     

Sea urchin sperm bioassay for sewage and chlorinated seawater and its relation to fish bioassays

Bioassays were conducted with sea urchin and sand dollar sperm to determine the toxicity of chlorinated and unchlorinated sewage effluent and chlorinated and brominated seawater. The sperm cells were exposed to seawater dilutions of each toxicant for 5–15 min. The fertilisation of eggs served as the indicators of sperm viability. The effective concentrations which reduced fertilisation success by 50% (EC50) averaged 2·2 and 4·8% chlorinated and unchlorinated sewage in seawater, respectively. The sperm cells were extremely sensitive to chlorinated seawater at concentrations from 0·002 to 0·020 mg/litre total residual oxidant (TRO). Brominated seawater proved toxic to sperm in one test at 0·015 mg/litre TRO. Results of the sperm bioassays are compared with previous acute and chronic bioassays with fish.     

Editorial

A flow-through system for exposure of seagrass to pollutants is described. Sea water with dissolved atrazine or PCP (pentachlorophenol) was pumped through a sealed 2-litre volume glass exposure vessel that contained either whole plants or leaves of Thalassia testudinum. Effects of the compounds on oxygen evolution and uptake by leaves were measured after exposure for 40 and 88 h. Rate of oxygen evolution was depressed strongly after 40 h by 1 ppm of atrazine or PCP. The rate of oxygen uptake was slightly depressed by atrazine but strongly depressed by PCP. Photosynthesis/respiration ratios were depressed to less than one by 1 ppm of atrazine or PCP and by 0·5 ppm atrazine. EC₅₀ values based upon depression of oxygen evolution after 40 hours exposure were: atrazine, 0·32 ppm PCP, 0·74 ppm. The data suggest that leaves may recover from, or adapt to, the presence of either toxicant.     

Phenolics in aquatic ecosystems: A selected review of recent literature

This review surveys the pertinent literature on phenolics in the aquatic ecosystem. Approximately 2% of the total organics manufactured in the US were phenols. Of the total phenolics produced in the US, 96% were synthetic and 4% were naturally occurring. Synthetic phenols arise from coking of coal, gas works and oil refineries, chemical plants, pesticide plants, wood preserving plants and dye manufacturing plants. Natural phenolics occur from aquatic and terrestrial vegetation and much of this is released by the pulp and paper industry.Toxicity of phenolics has been studied on selected microbes (e.g. protozoa, yeast and bacteria), algae, duckweed, and numerous invertebrates and vertebrates. Depending on the organism tested, the acute toxicity of phenol varies from 6·5 to 1840 mg/litre phenol. For other phenolics toxicity ranges from 0·084 to 555 mg/litre. The toxicity of phenolics varies with the type, position and number of substitutions on the parent molecule. Environmental factors affect the toxicity of phenolics and these include photolytic action, microbial degradation, pH, water hardness and temperature. Based on limited data, toxicity of phenolics may be less in continuous flow tests than in their sensitivity to phenolics as does the presence of oxygen. A seasonal factor may also affect the sensitivity of various fish. Starvation and lack of suitable substrate for bottom fauna increases organism sensitivity to phenol. The source of test animals may affect their sensitivity to phenolics and this effect may be due to short-term physiological acclimation and genetic selection.Studies on the biological effects of phenolics are limited and varied. Fish development and embryo survival were not affected by phenol levels less than 25 mg/litre. Amphibian embryos were sensitive to 0·5 mg/litre phenol. Pentachlorophenols inhibited fish growth at levels down to 1·74, μg/litre.Exposure of fish to phenol in concentrations as low as 4 mg/litre caused haemorrhaging at the base of the fins. Two hour exposure to 6·5 mg/litre phenol caused disruption of blood vessel walls and gill epithelium. Oedema and blood infiltration was a common effect observed in most major tissues studied from fishes exposed to phenol. Phenol, at 12·5 mg/litre, reduces the levels of neurohormones in fish exposed for 10 days. The effects of pentachlorophenol on blood glucose and blood lactate levels, and in vivo and in vitro activity levels of seven liver enzymes of eels are discussed. Pentachlorophenol, at 1·8 μg/litre, decreased assimilation conversion efficiency in underyearling salmon. Phenol also affects immunoglobin levels, blood protein levels and tissue micro-element levels. Feeding rates are affected by phenolics. Phenolics affect oxygen consumption rates and the effect may be on uncoupling of oxidative phosphorylation with a subsequent reduction of ATP formation.Many aspects of behaviour are affected by phenolics and the phases of ‘intoxication’ leading to death have been described for fish and invertebrates.Fish detoxify phenolics by forming conjugate glucuronides and sulphates. Body burdens of phenolics varied with exposure time and exposure concentration. When fish pre-exposed to phenol are transferred to clean water, body burdens drop up to 90% after three to four hours. Depuration rates for other phenolics took longer; up to 30 days for pentachlorophenol.Little research has been done on the cycling of phenol and phenolics (other than pesticides) in aquatic ecosystems. Microbial degradation will decompose phenolics rapidly if suitable bacteria are present. Other factors affecting the loss of phenolics from aquatic ecosystems include photolysis, adsorption and dilution. Phenol entering subterranean aquifers may not dilute or degrade very quickly. In one documented case well-water levels up to 200 mg/litre were measured 18 months after a spill.     

Effects of heavy metals on the development and survival of abalone Haliotis midae larvae

Despite a growing abalone Haliotis midae industry in South Africa, few studies have measured the effects of heavy metals on larval survival and growth in the face of recent increases in marine pollution. The aim of this study was to quantify the effect of copper on survival and zinc on development of H. midae larvae. Larvae 24 hours old were exposed to either copper (0–30 μg l^–1) or zinc (0–200 μg l^–1) for 48 h before mortality or larval development respectively were quantified. Copper significantly reduced survival, with an LC₅₀ of 5.58 μg l^–1 (5.07–6.15, 95% CI). Although the concentrations of zinc used in the study did not have a significant effect on mortality, there was a significant effect on the incidence of abnormal larvae with an EC₅₀ of 102.25 μg l^–1 (96.68–105.94, 95% CI). At concentrations above the EC₅₀, more than 50% of the larvae showed severe developmental abnormalities. Results suggest that copper poses the greatest risk to abalone larvae as the LC₅₀ was similar to the target concentration for this metal for South African coastal waters. By contrast, zinc is potentially less problematic, with the EC₅₀ for larval development being four times the target concentration for this metal.     

Rapid narcosis and delayed mortality in larvae of king crabs and kelp shrimp exposed to the water-soluble fraction of crude oil

Sensitivity of larval Paralithodes camtschatica and Eualus suckleyi exposed 20 min–96 h to the water-soluble fraction (WSF) of crude oil was determined. Swimming cessation in half the animals occurred within 20 minutes' exposure to 2 ppm WSF for shrimp larvae and only 0·5 ppm for crab larvae. Half the larvae of both species died after 6 hours' exposure to 8 ppm or 24 hours' exposure to 2–4 ppm, but deaths did not occur until several days after exposure ended. In the field, most non-swimming larvae would probably die as well.     

Acute toxicity of a used chrome lignosulphonate drilling mud to several species of marine invertebrate

The acute toxicity of a used seawater chrome lignosulphonate drilling mud to several species of marine annelids, crustaceans and molluscs was evaluated. The medium density mud (13·4 lb/gal, 1·57 kg/litre) was composed primarily of seawater, bentonite clay, chrome lignosulphonate, lignite, sodium hydroxide and barium sulphate. The toxicity of four mud/seawater preparations was determined. These were the layered solids phase (LSP), the suspended solids phase (SSP), the unfiltered mud aqueous fraction (MAF) and the filtered mud aqueous fraction (FMAF). Four species each of marine annelids and bivalve molluscs and five species of marine crustaceans were evaluated. The median lethal concentration of the MAF (96-h LC₅₀) varied from 32 to > 100% MAF for the different species. The FMAF was slightly less toxic than the MAF. Adult polychaetes, Neanthes arenaceodentata and Ctenodrilus serratus, one-day old juveniles of opossum shrimp, Mysidopsis almyra, and four day zoeae of grass shrimp, Palaemonetes pugio, were the most sensitive to the MAF. Juvenile N. arenaceodentata, adult polychaetes, Ophryotrocha labronica, and three bivalve molluscs were highly tolerant to the MAF. The SSP preparation at concentrations of 10-20 ml/litre was toxic to post-larvae and juveniles of the commercial shrimp, Penaeus duorarum and P. aztecus, respectively. Exposure to the LSP preparation caused greater than 50% mortality amongst adult N. arenaceodentata, juvenile and adult coquina clams, Donax variabilis texasiana and adult scallops, Aequipecten amplicostatus. Other species tested were quite tolerant. A sublethal response observed was the inhibition of reproduction in the marine annelids, Dinophilus sp. and Ctenodrilus serratus. Toxicity of the mud aqueous fractions appeared to be due primarily to volatile soluble organic materials in the extract, whilst that of the SSP and LSP preparations appeared to be due to the smothering action of fine particulates in the mud. Based on the results of this investigation and published observations of solids concentrations in the water column during drilling mud discharge, it is concluded that discharge of a used chrome lignosulphonate drilling mud, such as that used in the present investigation, from offshore platforms is not likely to cause measureable damage to benthic, demersal or pelagic marine animals.     

Some effects of certain metals on development and mortality within the moult cycle of crangon crangon (L.)

Crangon crangon (L.) (Crustacea: Decapoda) were subjected to three metals (Cd, Cu and Zn) at respective concentrations (0·35, 1·6 and 14·4mg/litre) that would induce 50% mortality in 5–6 days. Significantly different (P < 0·05) rates of mortality occurred in the three groups, although their ET₅₀'s were almost identical. No moultstage-dependent mortality was observed for Cd, but in Cu and Zn the post-moult stages (A and B) were more susceptible than either the intermoult (C_a and C_b) or premoult (D₀–D₄) stages.No significant (P> 0·05) sex- or size-dependent mortality was evident at the tested concentrations of these metals.Feeding and ecdysis were inhibited in all metals after day 3 and development from one moult-stage to the next was greatly reduced in Cd.Possible modes of toxicity have been discussed in terms of the physiological condition inferred from the moult-stage at the time of death.