Chemical and biological availability of sediment-sorbed benzo[a]pyrene and hexachlorobiphenyl

This study examined the chemical and biological availability of two nonpolar organic compounds, benzo[a]pyrene (BaP) and hexachlorobiphenyl (HCBP), from a spiked sediment that was aged for varying amounts of time. Chemical availability was evaluated using four different solvent combinations to extract chemicals from the sediment. The extractability of BaP and HCBP from sediment using traditional solvents was then compared to the transfer efficiency (TE) of a benthic invertebrate (Lumbriculus variegatus) to relate chemical extractability to bioavailability in the organisms. Results indicated that water was the solvent that best approximated bioavailability for BaP, whereas comparisons for HCBP were inappropriate, because TE values exceeded 100%. The inability to obtain a reasonable TE estimate for HCBP was most likely due to the fact that the oligochaetes received a major portion of their uptake from interstitial water instead of ingestion of sediment particles, which invalidated an important assumption of the TE model. Overall, the results of this study indicate that exhaustive chemical extractions may be an inaccurate representation of the bioavailable fractions for some contaminants.     

Lethal and sublethal effects of low dissolved oxygen condition on two aquatic invertebrates, Chironomus tentans and Hyalella azteca

Low dissolved oxygen (DO) conditions occur frequently during sediment toxicity testing, with potentially adverse effects on test organisms. The present study addressed the current lack of good information regarding low DO thresholds for toxicity tests using two common test species, juvenile Hyalella azteca and Chironomus tentans larvae. Results indicated that H. azteca was less tolerant of hypoxia than C. tentans. The 10-d highest- and no-observed-effect concentrations (HOEC and NOEC, respectively) for H. azteca were 1.2 +/- 0.1 and 2.9 +/- 0.1 mg/L DO, respectively. The 10-d NOEC for C. tentans was 1.2 +/- 0.1 mg/L DO, the lowest test concentration. Mortality was the predominant response of H. azteca to low DO exposure, with changes in growth and positioning behavior only evident at lethal DO concentrations. Although exposure to 1.2 +/- 0.1 mg/L DO for 10 d did not affect C. tentans survival or growth, significant behavioral changes were evident at 2.0 +/- 0.1 mg/L DO or less. Overall, the present results indicate that the North American guidelines for low DO thresholds during 10-d toxicity tests seem reasonable for juvenile H. azteca. However, the Environment Canada Guideline (3.4 mg/L DO at 23 degrees C) may be considered to be conservative for 10-d toxicity testing with C. tentans if only short-term effects on survival and growth are considered.     

Response spectrum of pentachlorobenzene and fluoranthene for Chironomus tentans and Hyalella azteca

The whole-body residues of pentachlorobenzene (PCBz) and fluoranthene (FLU) in Hyalella azteca and Chironomus tentans were determined for a variety of chronic sublethal effects. The endpoints evaluated for H. azteca included 28-d growth and survival and 42-d growth, survival, and reproduction. Adverse effects to C. tentans also were determined at multiple endpoints including 10-d growth, cumulative pupation and emergence, and reproduction. The lowest-observed-effect residue (LOER) based on whole-body residues associated with growth was consistent between compounds and species tested with concentrations ranging from 0.17 to 0.33 micromol/g. For H. azteca, the most sensitive endpoints were growth at 0.23 micromol/g and reproduction at 0.11 micromol/g for PCBz and FLU, respectively. For C. tentans, the most sensitive endpoints were emergence, development and reproduction at 0.02 micromol/g, and development and reproduction at 0.15 micromol/g for PCBz and FLU, respectively. Compared to residues associated with acute lethality, the most sensitive sublethal endpoints were approximately 4 and 60 times lower for PCBz and FLU, respectively. The relative consistency of the sublethal endpoints suggests that body residues can be a valuable tool to evaluate bioaccumulation data as part of a risk assessment to predict adverse effects to biota.     

Chronic toxicity of the synthetic hormone 17alpha-ethinylestradiol to Chironomus tentans and Hyalella azteca

The chronic toxicity of the synthetic hormone 17alpha-ethinylestradiol (EE2) was investigated in two benthic invertebrates, the midge Chironomus tentans and the freshwater amphipod Hyalella azteca, in life-cycle water-only assays. In C. tentans, a 50% decrease in emergence was observed at a concentration of 1.5 mg/L; emergence was a more sensitive endpoint than survival, growth, or biomass. Reproduction was not significantly affected by EE2 exposure until a concentration of 3.1 mg/L, where emergence, and therefore reproduction, did not occur. In contrast, reproduction was the most sensitive endpoint in H. azteca (50% decrease in reproduction observed at a concentration of 0.36 mg/L). The sensitivity of the F1 generation to EE2 was also investigated with H. azteca, but was not different from the F0 generation. The data from the present study were combined with those from previous 10-d toxicity assays, to derive acute to chronic toxicity ratios (ACRs) for EE2. The ACRs calculated for EE2 were 13 for C. tentans and 16 for H. azteca, indicating that the application factors currently used in ecological risk assessment for the derivation of chronic toxicity are protective and conservative for these organisms. The results of the present study suggest that chronic toxicity was not mediated by disruption of endocrine pathways. Using a hazard quotient approach, the risk associated with sublethal exposure to EE2 was <1 for H. azteca and C. tentans, indicating that adverse effects are not expected, and that environmental exposure to EE2 likely poses a low risk to benthic invertebrates.     

Interlaboratory evaluation of Hyalella azteca and Chironomus tentans short-term and long-term sediment toxicity tests

Methods for assessing the long-term toxicity of sediments to Hyalella azteca and Chironomus tentans can significantly enhance the capacity to assess sublethal effects of contaminated sediments through multiple endpoints. Sublethal tests allow us to begin to understand the relationship between short-term and long-term effects for toxic sediments. We present an interlaboratory evaluation with long-term and 10-d tests using control and contaminated sediments in which we assess whether proposed and existing performance criteria (test acceptability criteria [TAC]) could be achieved. Laboratories became familiar with newly developed, long-term protocols by testing two control sediments in phase 1. In phase 2, the 10-d and long-term tests were examined with several sediments. Laboratories met the TACs, but results varied depending on the test organism, test duration, and endpoints. For the long-term tests in phase 1, 66 to 100% of the laboratories consistently met the TACs for survival, growth, or reproduction using H. azrteca, and 70 to 100% of the laboratories met the TACs for survival and growth, emergence, reproduction, and hatchability using C. tentans. In phase 2, fewer laboratories participated in long-term tests: 71 to 88% of the laboratories met the TAC for H. azteca, whereas 50 to 67% met the TAC for C. tentans. In the 10-d tests with H. azteca and C. tentans, 82 and 88% of the laboratories met the TAC for survival, respectively, and 80% met the TAC for C. tentans growth. For the 10-d and long-term tests, laboratories predicted similar toxicity. Overall, the interlaboratory evaluation showed good precision of the methods, appropriate endpoints were incorporated into the test protocols, and tests effectively predicted the toxicity of sediments.     

Sediment Toxicity Evaluation for Hexachlorobenzene: Spiked Sediment Tests with Leptocheirus plumulosus, Hyalella azteca, and Chironomus tentans

Hexachlorobenzene (HCB) is a hydrophobic organic chemical that has shown a lack of toxicity in aquatic tests at concentrations up to and exceeding the solubility limit. The equilibrium partitioning approach to deriving sediment quality benchmarks, which assumes that toxicity can be predicted based on contaminant concentrations in interstitial water, predicts that HCB will not produce direct toxicity to benthic invertebrates as a sediment contaminant. However, the potential for toxicity due to direct exposure to sediment-adsorbed HCB has not been thoroughly established. This study evaluated the survival and growth of the estuarine amphipod Leptocheirus plumulosus, the freshwater amphipod Hyalella azteca, and the midge Chironomus tentans (freshwater) following 10-day exposure to sediment spiked with a range of HCB concentrations. H. azteca was tested under both freshwater and estuarine (10 ppt salinity) conditions. No significant toxicity was observed for any test species at the highest test concentration (60 mg/kg normalized to 1% organic carbon). Minimum detectable differences were less than or equal to 20% for three of eight test endpoints. The observed results add to the available weight of evidence indicating a limited potential for HCB-related sediment toxicity to benthic invertebrates. Received: 23 February 1998/Accepted: 8 June 1998     

Toxicokinetics of sediment-associated polybrominated diphenylethers (flame retardants) in benthic invertebrates (Lumbriculus variegatus, Oligochaeta)

Polybrominated diphenylethers (PBDEs) are ubiquitous environmental contaminants showing rapid temporal increase in some sample types. The compounds are known to biomagnify in aquatic food webs and are assumed to archive into sediments and soils. Currently, no direct evidence indicates whether sediment-associated PBDEs are available for biota. The aim of the present study was to explore the uptake and elimination of two common congeners (47 and 99) in sediment-inhabiting invertebrates to shed light on possible bioavailability of sediment-associated PBDEs. Two clean lake sediments were spiked with environmentally relevant concentrations of 14C-labeled tetra- and pentabromo diphenylether, and oligochaetes (Lumbriculus variegatus) were exposed for three or four weeks to allow kinetic accumulation calculations. Subsequent depuration tests were performed after three weeks of exposure to obtain depuration rates. Both congeners were clearly bioavailable, and only slight differences in steady-state tissue concentrations were found between the four sediment-ingesting oligochaete treatments (biota sediment accumulation factors [BSAFs], 3.0-3.7). The tetrabromo diphenylether-exposed oligochaetes that did not ingest sediment had clearly lower influx rates (0.1 vs 1-3 nmol h(-1)) than sediment-ingesting worms. Also, the estimated BSAF (1.8) was statistically different from that of the sediment-ingesting oligochaetes. These findings support the significance of feeding behavior in bioaccumulation of very hydrophobic organic contaminants. Depuration of both congeners was biphasic, indicating two kinetically different compartments in L. variegatus. Compartment A made up 73 to 92% of total radioactivity in tissues and had relatively fast depuration rates (half-lives, 10.5-47.5 h); the smaller compartment B had very slow depuration rates. No significant biotransformation of PBDEs was evident. The present study clearly demonstrates that the sediment-associated PBDEs, like other hydrophobic organic contaminants of environmental concern, are not totally sequestered from sediment-inhabiting oligochaetes and are subject to trophic transfer.     

Relationship between metabolism and bioaccumulation of benzo[a]pyrene in benthic invertebrates

The potential influence of polycyclic aromatic hydrocarbon (PAH) metabolism on bioaccumulation is well accepted, but rarely has been examined in many species of benthic invertebrates that commonly are found in contaminated sediments, or used in bioaccumulation or toxicity tests. In this study, the relative ability of 11 species of near-shore benthic invertebrates to metabolize and bioaccumulate a model PAH, benzo[a]pyrene (B[a]P), was evaluated. Species examined included six polychaetes (Clymenella torquata, Nereis virens, Nereis succinea, Nephtys incisa, Spio setosa and Cirriformia grandis), three bivalves, (Macoma balthica, Mya arenaria, and Mulinia lateralis), and two amphipods (Ampelisca abdita and Leptocheirus plumulosus). After 7 d of exposure to sediments spiked with radiolabeled B[a]P, metabolites comprised between 6.1% (Clymenella torquata) to 85.7% (Nereis succinea) of total accumulated B[a]P, with individual species from the same phylogenetic groups showing large differences in their ability to metabolize this PAH. Bioaccumulation factors (B[a]P in tissue/B[a]P in sediment) were inversely related to the species' ability to metabolize PAH, highlighting the importance of considering metabolism when interpreting bioaccumulation across several species. These data argue strongly against the continued use of the large polychaete Nereis virens, one of the species showing the greatest ability to metabolize B[a]P, for bioaccumulation testing when PAHs are being considered. Other commonly used test species had relatively low levels of metabolism (Ampelisca abdita, Leptocheirus plumulosus, and Macoma balthica), supporting their use in evaluation of potential PAH impact on the environment.     

Accumulation and food chain transfer of fluoranthene and benzo[a]pyrene in Chironomus riparius and Lepomis macrochirus

This research investigated the accumulation of polycyclic aromatic hydrocarbons (PAHs) by Chironomus riparius from sediments and transfer of these contaminants to bluegill, Lepomis macrochirus. Experiments were conducted in laboratory microcosms containing sediments spiked with either benzo[a]pyrene (BAP) or fluoranthene (FLU). Chironomids rapidly accumulated PAHs from sediments. Concentrations of BAP and FLU in chironomids increased with sediment concentration; however, FLU accumulated to a much greater extent. At sediment concentrations ranging from 47 to 4,040 g/kg, levels of FLU in chironomids ranged from below detection to 181,000 g/kg. In contrast, the maximum concentration of BAP measured in chironomids at similar sediment levels was 6,030 g/kg. Levels of FLU and BAP in bluegill that were fed contaminated chironomids were generally low, indicating either low uptake or rapid metabolism of these compounds.Bioturbation of sediments by chironomids decreased water clarity and released sediment-associated BAP to overlying water. BAP in water and in C. riparius increased significantly with chironomid density. In experiments where bluegill were exposed to BAP from water, direct contact with sediments, and chironomids, each source contributed to total body burden. The results of the experiments indicated that PAHs in sediments may be mobilized and made available to benthic invertebrates and fish.     

Toxicity of silver in water and sediment to the freshwater amphipod Hyalella azteca

Hyalella azteca was exposed to Ag as AgNO3 over a 10-d period in water and two lake sediments that were selected on the basis of their differences in metal-binding properties. The median lethal concentrations (LC50s) for waterborne exposures were 5.4 and 4.9 microg/L for total and dissolved Ag, respectively. In the sediment containing a lesser quantity of total Ag-binding ligands (i.e., Bond Lake, Douglas County, WI, USA, sediment), an Ag-amended sediment toxicity test resulted in a 10-d LC50 of 0.084 g (i.e., 84,000 microg) Ag/kg dry sediment or 8.6 microg Ag/L of pore water (PW). The no-observed-effect concentration (NOEC) to lowest-observed-effect concentration (LOEC) range was 0.012 to 0.031 g Ag/kg dry sediment, or less than 5.0 to 6.0 microg Ag/L of PW. In the sediment with a greater quantity of total Ag-binding ligands (i.e., West Bearskin Lake, Cook County, MN, USA, sediment), the 10-d LC50 was 2.98 g Ag/kg dry sediment, and the NOEC to LOEC range was 2.15 to 4.31 g Ag/kg dry sediment. Because "dissolved" concentrations of Ag in PW were less than 5.0 microg/L at the critical exposures in the latter test, the bioavailable and toxic form of Ag may have been a weakly associated coprecipitate or colloidal complex with hydrous iron oxides that competitively partitioned to the surface of the gills.     

Bioconcentration and depuration of copper, cadmium, and zinc mixtures by the freshwater amphipod Hyalella azteca

The uptake and elimination of copper (Cu), cadmium (Cd), and zinc (Zn) by the amphipod Hyalella azteca during exposure to the metals singly and in various combinations was examined in controlled laboratory experiments. In single metal exposures the accumulation of all metals was rapid and increased with exposure time. Copper elimination was slower compared to that for zinc and for cadmium no elimination was detected after 5 days in clean water. In the two-metal mixtures it appears that the presence of one metal influenced the bioconcentration of the other, since the bioconcentration factor (BCF) for copper was higher in the presence of cadmium than in the presence of zinc and in the case of cadmium, the decrease of K(1) values from cadmium single exposure to the binary and tertiary mixtures suggests possible inhibition of cadmium uptake by the other metals. In the case of the three-metal mixture the situation is less clear, with both increased and decreased BCFs recorded, in comparison to single-metal and two-metal mixtures, suggesting both stimulation and inhibition of metal accumulation.     

Uptake and accumulation of sediment-associated 4-nonylphenol in a benthic invertebrate (Lumbriculus variegatus, freshwater oligochaete)

In the present work, the oligochaete Lumbriculus variegatus was exposed for 56 d to lake sediment spiked with 4-nonylphenol (4-NP), which is a breakdown product of alkylphenol polyethoxylates, an important class of nonionic surfactants. During the exposure period, the content of 4-NP was determined in the oligochaetes, sediment, overlying water, and pore water in order to monitor the distribution of the 4-NP in the compartments of the test system. Concentration of 4-NP in L. variegatus increased linearly over the course of the test, with an uptake rate coefficient of 1.9 x 10(-2) (+/- 0.2 x 10(-2); [g carbon/(g lipid x h)]). No steady state was reached at the end of the exposure period, suggesting that the elimination of 4-NP by the organism was negligible. Ingested sediments played an important role in the accumulation of 4-NP in L. variegatus, which may achieve very high 4-NP body concentrations. The 56-d biota sediment accumulation factor (BSAF) was 24 +/- 7 g carbon/g lipid. L. variegatus also was exposed to 4-NP-contaminated field sediment, and field oligochaetes and sediments were collected for 4-NP pollution assessment in aquatic ecosystem. The 4-NP uptake with natural sediment was in accordance with that measured with spiked sediments, suggesting that the bioavailability of sediment-associated 4-NP for L. variegatus was not affected by 4-NP sediment concentration and abiotic sediment characteristics. The BSAFs measured in field oligochaetes, ranging from 39 to 55 g carbon/g lipid, was relatively higher than the bioaccumulation factor measured in laboratory tests. The results suggest that 4-NP concentration can reach high levels in benthic oligochaetes; this can be an important way of exposure for their pelagic predators.     

Toxicity of the explosives 2,4,6-trinitrotoluene,hexahydro-1,3,5-trinitro-1,3,5-triazine,and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine in sediments to Chironomus tentans and Hyalella azteca: low-dose hormesis and high-dose mortality

The toxicity of the explosives 2,4,6-trinitrotoluene (TNT); hexahydro-1,3,5-trinitro-1,3,5-triazine (royal demolition explosive [RDX]); and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (high-melting explosive [HMX]), was evaluated in spiked sediment with two freshwater invertebrates. The midge Chironomus tentans and the amphipod Hyalella azteca demonstrated significant toxic effects after exposure to TNT and its degradation products, 1,3,5-trinitrobenzene (TNB) and 2,4-diamino-6-nitrotoluene (2,4-DANT). Significant reductions in survival of C. tentans exposed to TNT, TNB, and 2,4-DANT were observed at nominal sediment concentrations as low as 200 mg/kg. Hyalella azteca was more sensitive to TNT, TNB, and 2,4-DANT than the midge, where significant reductions in survival were observed at nominal concentrations of 50, 100, and 200 mg/kg, respectively. Survival of the midge and the amphipod was unaffected after exposure to RDX or HMX at the highest concentrations of 1,000 and 400 mg/kg, respectively. Growth of the midge, measured as total weight, was significantly reduced by 2,4-DANT. However, significantly increased growth was observed after exposure to sublethal concentrations of RDX and HMX. Although significant reductions in amphipod survival were observed at high concentrations of TNB, growth was significantly increased at sublethal concentrations. The results of the current investigation suggest that organisms exposed to explosives at contaminated sites may be affected at concentrations less than 25 mg/kg through hormetic growth enhancement and at higher concentrations through increased mortality.     

Chronic toxicity of lead to three freshwater invertebrates--Brachionus calyciflorus, Chironomus tentans, and Lymnaea stagnalis

Chronic lead (Pb) toxicity tests with Brachionus calyciflorus, Chironomus tentans, and Lymnaea stagnalis were performed in artificial freshwaters. The no-observable-effect concentration (NOEC), lowest-observable-effect concentration (LOEC), and calculated 20% effect concentration (EC20) for the rotifer B. calyciflorus were 194, 284, and 125 microg dissolved Pb/L, respectively. The midge C. tentans was less sensitive, with NOEC and LOEC of 109 and 497 microg dissolved Pb/L, respectively, and the snail L. stagnalis exhibited extreme sensitivity, evident by NOEC, LOEC, and EC20 of 12, 16, and < 4 microg dissolved Pb/L, respectively. Our findings are presented in the context of other reports on chronic Pb toxicity in freshwater organisms. The L. stagnalis results are in agreement with a previous report on pulmonate snails and should be viewed in the context of current U.S. Environmental Protection Agency (U.S. EPA) hardness adjusted water quality criteria of 8 microg Pb/L. The present findings and earlier reports indicate that freshwater pulmonate snails may not be protected by current regulatory standards. Measurements of whole-snail Na+ and Ca2+ concentrations following chronic Pb exposure revealed that Na+ homeostasis is disturbed by Pb exposure in juvenile snails in a complicated pattern, suggesting two physiological modes of action depending on the Pb exposure concentration. Substantially reduced growth in the snails that exhibit very high Ca2+ requirements may be related to reduced Ca2+ uptake and thereby reduced shell formation.     

双壳类水产品中(+)-anti-BPDE-DNA加合物HPLC/FD检测

目的 建立检测双壳类水产品中（+）-反-7,8-二羟基-9,10-环氧苯并（a）芘（BPDE）-DNA加合物的高效液相色谱荧光法（HPLC/FD）。方法 用组织基因组DNA提取试剂盒提取6种双壳类水产品组织中的DNA,0.1 mol/L HCl 、90 ℃酸解4 h,乙酸乙酯充分萃取酸解产物——苯并（a）芘-四醇。以CenturySIL C18-BDS色谱柱（150 mm×4.6 mm,5 μm）分离;洗脱流动相：V（甲醇）/V（水）=55/45;流速：1.0 mL/min;进样量：20 μL;激发波长：265 nm,发射波长：395 nm;荧光检测苯并（a）芘-四醇的含量。结果 该方法的检测限为0.3 ng/mL,在0.5~100 ng/mL范围内呈良好的线性关系（r²=0.9960）;日内相对标准偏差（RSD）为2.8%~4.2%,日间RSD为3.2%~5.8%;双壳类水产品中（+）-anti-BPDE-DNA含量为13.44~152.7 μg/kg,RSD为3.0%~6.5%;加标回收率为86.9%~91.6%,RSD为3.1%~7.3%。结论 该法简便、快速、灵敏度高,可用于双壳类水产品中（+）-anti-BPDE-DNA加合物的检测。     

苯并[a]芘在大鼠脑组织中分布动态观察

目的 观察[¹⁴C]标记苯并[a]芘在大鼠脑内的分布。方法 将100只SD大鼠随机分为对照组和实验组,实验组尾静脉注射[¹⁴C]标记苯并[a]芘3.7×10⁵Bq/kg,对照组注射等量生理盐水;在注射后1,6,12,24和48 h用光镜放射自显影法观察苯并[a]芘在脑内的分布情况。结果 与对照组比较,实验组大鼠脑组织注药后1 h即有苯并[a]芘银粒出现,随着时间的增加,银粒数也逐渐增加,24 h达高峰,48 h明显减少,注射后1,6,12,24,48 h银粒数分别为(17.68±1.79),(22.67±2.15),(25.79±2.55),(32.33±2.78),(18.01±1.68)粒,差异有统计学意义(F=69.67,P<0.01);银粒在脑中分布不均匀,注药后1 h主要集中在海马,6 h主要集中于大脑皮层,12 h则分布于纹状体;各时相脑组织中神经元银粒数明显高于神经胶质细胞(P<0.05)。结论 苯并[a]芘在各脑区的分布不均匀,24 h达到高峰,神经元细胞可能是苯并[a]芘靶细胞。     

Toxicity of uranium, molybdenum, nickel, and arsenic to Hyalella azteca and Chironomus dilutus in water-only and spiked-sediment toxicity tests

A series of laboratory spiked-sediment toxicity tests with the amphipod Hyalella azteca and the midge Chironomus dilutus were undertaken to determine acute and chronic toxicity thresholds for uranium (U), molybdenum (Mo), nickel (Ni), and arsenic (As) based on both whole-sediment (total) and pore water exposure concentrations. Water-only toxicity data were also generated from separate experiments to determine the toxicities of these metals/metalloids under our test conditions and to help evaluate the hypothesis that pore water metal concentrations are better correlated with sediment toxicity to benthic organisms than whole-sediment metal concentrations. The relative toxicity of the four elements tested differed depending on which test species was used and whether whole-sediment or pore water metal concentrations were correlated with effects. Based on measured whole-sediment concentrations, Ni and As were the two most acutely toxic elements to H. azteca with 10-d LC50s of 521 and 532 mg/kg d.w., respectively. Measured pore water concentrations indicated that U and Ni were the two most acutely toxic elements, with 10-d LC50s to H. azteca of 2.15 and 2.05 mg/L, respectively. Based on pore water metal concentrations, the no-observed-effect concentrations (NOECs) for growth were (H. azteca and C. dilutus, respectively) 0.67 and 0.21 mg/L for U, <0.37 and 0.60 mg/L for Ni, and 16.43 and <0.42 mg/L for As. Pore-water lowest-observed-effect concentrations (LOECs) for growth were (H. azteca and C. dilutus, respectively) 2.99 and 0.48 mg/L for U, 0.37 and 2.33 mg/L for Ni, and 58.99 and 0.42 mg/L for As. For U and Ni, results from 96-h water-only acute toxicity tests correlated well with pore water metal concentrations in acutely toxic metal-spiked sediment. This was not true for As where metalloid concentrations in overlying water (diffusion from sediment) may have contributed to toxicity. The lowest whole-sediment LOEC reported here for As was 6.6- and 4-fold higher than the Canadian Council of Ministers of the Environment interim sediment quality guideline and the Canadian Nuclear Safety Commission (CNSC) lowest effect level (LEL), respectively. The lowest whole-sediment LOECs reported here for Ni, U and Mo were 4-, 17.5-, and >260-fold higher, respectively, than the CNSC LELs for these metals/metalloids. Data on pore water metal concentrations in toxic sediment would be a useful addition to future Guidelines documents.     

Vitamin A status and metabolism of benzo[a]pyrene in the rat

Male Sprague-Dawley rats were maintained on a vitamin A-deficient diet for a period of five weeks. At the end of that time, hepatic cytochrome P450 levels in vitamin A-deficient rats were 65% that of rats fed a complete diet. However, the hepatic rate of benzo[a]pyrene metabolism was significantly greater (2 times) in vitamin A-deficient rats compared with those fed a complete diet. The pattern of metabolites separable by thin-layer chromatography was similar in both groups of rats. Benzo[a]pyrene induced its own metabolism by a slightly greater amount in the vitamin-sufficient rats, but it was not to the level of the deficient group, although the levels of cytochrome P450 were still below those of the deficient rats. In discussing lung microsomes, benzo[a]pyrene pre-treatment of deficient rats resulted in slightly elevated levels of cytochrome P450 and a slightly greater rate of metabolism of benzo[a]pyrene compared with rats fed the complete diet.