Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Archives of Environmental Contamination and Toxicology (v.45, #1)
Use of a Coupled Biological System to Treat a Chemically Complex Air Stream by M. R. Manninen; B. A. Niemi; G. T. Kleinheinz (pp. 0001-0010).
The use of biological systems to remove contaminants from waste streams has been well documented. However, when dealing with complex waste streams, the use of one biological treatment system may not be the best alternative. When treating a complex waste stream, the use of “treatment trains” or “coupled systems” may be advantageous compared with any single biological technology. This article demonstrated that a coupled system was effective in biodegrading a chemically complex mixture of volatile organic compounds (VOCs). A bench-scale system consisting of a liquid bioreactor and a biofilter was used for the biodegradation of acetone, methanol, methyl ethyl ketone, naphthalene, alpha-pinene, and toluene. The bioreactor contained an inert solid support that immobilized a microbial population. The biofiltration portion of the system utilized the same microbial inoculum but employed Douglas fir bark as its solid support. Successful biodegradation of the complex VOC mixture was accomplished with this coupled system with an average VOC removal efficiency of 96% and VOC loading rates as high as 79 g/m3/h for inlet concentrations of > 8,000 ppmv. At elevated flow rates the liquid reactor demonstrated limited removal of some compounds, such as alpha-pinene and toluene, while maintaining excellent removal of other compounds, such as methanol and acetone. The biofilter portion of the system proved very successful in degrading the remaining toluene and alpha-pinene, thus complementing the removal from the bioreactor. This study demonstrates that coupled biological systems may be utilized for a chemically complex VOC-laden air stream that previously may not have been considered for biological treatment.
Mercury and Other Trace Elements in Sediment Cores from Central Texas Lakes by N. Menounou; B. J. Presley (pp. 0011-0029).
Metals released during fossil fuel use are important atmospheric pollutants. Mercury and other trace metals can be transferred to an aquatic environment through atmospheric deposition. In the work reported here, a number of sediment cores were retrieved from central Texas lakes in the proximity of a coal-fired power plant in search of local anthropogenic effects. Cores were collected along a transient parallel to the prevailing wind direction (S-SE) in the area. Trace element concentrations in the lignite and in effluents from the power plant showed that some elements remained constant (Al, Cu) throughout the different lignite combustion and power production processes. Some (like Cd and Se) showed an affinity for the smaller particles, whereas others (Hg) showed very low concentrations in all the solid wastes, indicating that they probably escaped with the flue gases. Sediment cores from a lake next to the power plant showed higher trace metal concentration in the upper part of the cores (more recent sediment). For example, there was as much as a tenfold increase in Hg concentration between the core bottom (10 ng/g), where the sediment was approximately 100 years old and the surface (100 ng/g). Cd and Se at surface sediments were also found to be as high as 1.6 and 3.45 µg/g, respectively. The excess metal inventory was higher for the lakes located next to the power plant than for two lakes about 30 km away.
Trace Organic Contaminants, Including Toxaphene and Trifluralin, in Cotton Field Soils from Georgia and South Carolina, USA by K. Kannan; S. Battula; B. G. Loganathan; C.-S. Hong; W. H. Lam; D. L. Villeneuve; K. Sajwan; J. P. Giesy; K. M. Aldous (pp. 0030-0036).
Residues of organic contaminants—including toxaphene, DDT, trifluralin, hexachlorocyclohexanes, polychlorinated biphenyls, polycyclic aromatic hydrocarbons (PAHs) and nonylphenol—were measured in 32 cotton field soils collected from South Carolina and Georgia in 1999. Toxaphene, trifluralin, DDT and PAHs were the major contaminants found in these soils. The maximum concentration of toxaphene measured was 2,500 ng/g dry weight. Trifluralin was detected in all the soils at concentrations ranging from 1 to 548 ng/g dry weight. Pesticide residues were not proportional to soil organic carbon content, indicating that their concentrations were a reflection of application history and dissipation rates rather than air–soil equilibrium. Soil extracts were also subjected to in vitro bioassays to assess dioxinlike, estrogenic, and androgenic/glucocorticoid potencies. Relatively more polar fractions of the soils elicited estrogenic and androgenic/glucocorticoid activities, but the magnitude of response was much less than those found in coastal marine sediments from industrialized locations.
Assessment of Effects of Chromated Copper Arsenate (CCA)—Treated Timber on Nontarget Epibiota by Investigation of Fouling Community Development at Seven European Sites by C. J. Brown; R. A. Eaton; S. M. Cragg; P. Goulletquer; A. Nicolaidou; M. J. Bebianno; J. Icely; G. Daniel; T. Nilsson; A. J. Pitman; G. S. Sawyer (pp. 0037-0047).
To assess the effect of the anti–marine-borer timber preservative CCA (a pressure-impregnated solution of copper, chromium, and arsenic compounds) on nontarget epibiota, fouling community development was investigated. Panels of Scots pine treated to target retentions of 12, 24, and 48 kg CCA per m3 of wood (covering the range of retentions recommended for marine use) plus untreated controls were submerged at seven coastal sites (Portsmouth, UK; La Tremblade [two sites], France; Ria Formosa, Portugal; Sagres, Portugal; Kristineberg, Sweden; Athens, Greece). The fouling community on the surfaces of the panels was assessed both qualitatively and quantitatively after 6, 12, and 18 months of exposure. Multivariate statistical methods were used to compare community structure between panel treatments. Panels treated to the three CCA loadings supported very similar fouling assemblages, which in most cases had higher numbers of taxa and individuals than assemblages on untreated panels. No detrimental effects on epibiota due to CCA preservatives were detected at any of the treatment levels at all seven exposure sites, suggesting that the range of environmental conditions at the sites had no bearing on preservative impact on fouling biota. Differences in community structure between CCA-treated and untreated panels may be due to enhanced larval settlement on CCA-treated timber by some species as a result of modifications to the surface properties of the timber by the preservative. Possible reasons for the higher numbers of certain species on the surface of CCA-treated panels are discussed.
Effects of Exposure Duration of Herbicides on Natural Stream Periphyton Communities and Recovery by K. Gustavson; F. Møhlenberg; L. Schlüter (pp. 0048-0058).
To improve risk estimates for herbicides in streams, the sensitivity of natural periphyton communities to four herbicides (metribuzin, hexazinone, isoproturon, and pendimethalin) was examined in experiments including varying exposure duration and a recovery phase. Effect parameters included assimilation of 14C and concentration of diagnostic pigments as proxies for photosynthetic activity and algal group composition, respectively. The results indicated that isoproturon, metribuzin, and hexazinone affected the photosynthetic activity of periphyton at distinctly lower concentrations than the effect concentrations published for standard single-species growth-tests with phytoplankton species. Pendimethalin did not show effects on the photosynthetic activity of periphyton at the concentrations tested. The effect concentration (EC50) of isoproturon and metribuzin decreased by one to two orders of magnitude when the duration of exposure increased from 1 h to 24 h, while hexazinone had a stimulating effect on the photosynthetic activity of periphyton after 1 h exposure and inhibiting effect after 24 h exposure. The photosynthetic activity after exposure to metribuzin for 1, 2, 6, 18, 23, or 48 h recovered almost completely after 48 h in herbicide-free water. However, different periphyton groups responded differently to metribuzin exposure: Chlorophytes were severely affected by exposure and did not recover, whereas diatoms and especially cyanobacteria recovered well. Overall the study showed that the effects of herbicides on periphyton are strongly affected by the duration of exposure, and even short-term exposure may have distinct effects on the periphyton community.
PCB-Induced Oxidative Stress in the Unicellular Marine Dinoflagellate Lingulodinium polyedrum by M. A. da S. Leitão; K. H. M. Cardozo; E. Pinto; P. Colepicolo (pp. 0059-0065).
The susceptibility of the dinoflagellate Lingulodinium polyedrum to Arochlor 1254, a commercial mixture of polychlorinated biphenyl (PCB) congeners was examined through toxicity bioassays based on cell survival and measures of oxidative balance and adaptive response to PCB stress. The highest Arochlor 1254 concentration that did not cause observed effects (NOEC) on cell growth was 100 (48 h) and 25 ppb (96 h). The concentration that caused maximum effect (MEC) was 300 ppb (48 h) and 250 ppb (µl L–1) (96 h). The concentrations that promoted 50% cell death (LC50) were 146 and 122 ppb after 48 and 96 h, respectively. The cell numbers were lower after 96 h of exposure than after 48 h, suggesting that neither recovery nor growth occurred.Under exposure to 120 ppb Arochlor 1254 for 48 h the oxidative damage in proteins was 121% higher than the control, as measured by reactive carbonyl levels, but no oxidative damage was found in lipids measured as malondialdehyde contents. Total superoxide dismutase (SOD) activity increased to plateau levels 146% greater than control values. The cells also exhibited increased ascorbate peroxidase (APx) activity (50%) and peridinin content (27%). No changes were observed in β-carotene under these experimental conditions. Therefore, SOD and APx induction and increased peridinin content may be principal primary adaptive responses to an increase of reactive oxygen species in Arochlor 1254 stress as indicated by protein oxidative damage and are an early marker of Arochlor 1254 contamination.
Derivation of Aquatic Screening Benchmarks for 1,2-Dibromoethane by L. A. Kszos; S. S. Talmage; G. W. Morris; B. K. Konetsky; T. Rottero (pp. 0066-0071).
Ethylene dibromide (1,2-dibromoethane or EDB) was primarily used in the United States as an additive in leaded gasoline and as a soil and grain fumigant for worm and insect control until it was banned in 1983. Historical releases of EDB have resulted in detectable EDB in groundwater and drinking wells, and recently concentrations up to 16 μg/L were detected in ground water at two fuel spill plumes in the vicinity of the Massachusetts Military Reservation Base on Cape Cod, Massachusetts. Because the ground water in this area is used to flood cranberry bogs for the purposes of harvesting, the U.S. Air Force sponsored the development of aquatic screening benchmarks for EDB. Acute toxicity tests with Pimephales promelas (fathead minnow), Daphnia magna, and Ceriodaphnia dubia were conducted to provide data needed for development of screening benchmarks. Using a closed test-system to prevent volatilization of EDB, the 48-h LC50s (concentration that kills 50% of the test organisms) for P. promelas, D. magna, and C. dubia were 4.3 mg/L, 6.5 mg/L, and 3.6 mg/L, respectively. The screening benchmark for aquatic organisms, derived as the Tier II chronic water quality criteria, is 0.031 mg EDB/L. The sediment screening benchmark, based on equilibrium partitioning, is 2.45 mg EDB/kg of organic carbon in the sediment. The screening benchmarks developed here are an important component of an ecological risk assessment, during which perhaps hundreds of chemicals must be evaluated for their potential to cause ecological harm.
Chemical Analysis and Sediment Toxicity Bioassays to Assess the Contamination of the River Lambro (Northern Italy) by R. Bettinetti; C. Giarei; A. Provini (pp. 0072-0078).
This study consisted of a 10-day whole sediment toxicity test with the chironomid Chironomus riparius and a 28-day sediment toxicity test with the oligochaete Tubifex tubifex at seven sites to assess the quality of the River Lambro (Italy), one of the most contaminated rivers of the Po Basin. Endpoints measured were survival and growth for chironomids and cocoon deposition and development of young worms for tubificid oligochaetes. Responses were evaluated in relation to the occurence of organic micropollutants (PCBs, DDT, HCB, and HCH) representative of the industrial and agricultural contamination of the area. Though survival of the organisms remained unaffected, sublethal effects were observed at all sites. The sediment sampled at the farthest upstream site differed from the control only in the number of cocoons deposited by the worms. Both test species in the next three sediments, where concentrations of PCB and DDT were in the range 21.9–39.5 ng g–1 DW and 0.6–1.3 ng g–1 DW, respectively, experienced greater toxicity in terms of growth and reproduction. Contamination was particularly high in the site closest to Milan, where the river receives untreated urban and industrial discharges. Levels of total PCBs and total DDT here were up to two orders of magnitude higher than those found at the other sampling locations, and chironomid growth and the reproductive endpoints of tubificids were significantly lower than in the control and the other sites. The test results for the next two stations showed improvement relative to that of Milan, although contamination was still evident. Sublethal effects were in agreement with the measured concentrations of the principal persistent organic pollutants and should be included as part of environmental monitoring efforts as a basis for assessing the recovery of the river.
A Comparison of the Daphnids Ceriodaphnia dubia and Daphnia ambigua for Their Utilization in Routine Toxicity Testing in the Southeastern United States by S. M. Harmon; W. L. Specht; G. T. Chandler (pp. 0079-0085).
U.S. regulatory agencies commonly require effluent toxicity testing with Ceriodaphnia dubia—a practice that has led to the criticism that this species and test protocol often does not reflect local taxa or site-specific conditions. Using an indigenous test species may produce a more realistic model of local effects and may minimize test endpoint variance due to regional differences in water quality. This study addressed the substitution of C. dubia with Daphnia ambigua for toxicity testing in the southeastern United States. This investigation determined that D. ambigua could be laboratory cultured with only minimal changes to established regulatory protocol and that the life-cycle characteristics of this species were conducive to traditional acute and chronic aquatic toxicity test methods used with other daphnids. Acute toxicity tests showed that D. ambigua was less sensitive to some toxicants (sodium chloride, copper sulfate, and sodium lauryl sulfate) but more sensitive to others (chlorpyrifos). Chronic tests with copper sulfate and sodium chloride resulted in lower EC50s for D. ambigua reproduction with both compounds. When exposed to low-alkalinity, low-pH stream waters typical of many southeastern United States watersheds, C. dubia demonstrated a significant reproductive depression in two of three streams tested, whereas D. ambigua experienced no chronic effect. These results suggest that D. ambigua may serve as a suitable surrogate for C. dubia as an toxicity indicator species in these types of receiving streams.
Metallothionein Induction in the RTH-149 Cell Line as an Indicator for Heavy Metal Bioavailability in a Brackish Environment: Assessment by RT-Competitive PCR by I. Kamer; J. Douek; M. Tom; B. Rinkevich (pp. 0086-0091).
Estuarine and marine near-shore environments are often subjected to heavy metal pollution. We establish a bioassay using the quantitative evaluation of metallothionein (MT) transcript in the fish hepatoma cell line, RTH-149, as a tool for detecting heavy metal pollution in brackish-marine water containing other pollutants in addition to heavy metals. RT-competitive polymerase chain reaction was used for the quantitative evaluation of the transcript in absolute units. Cadmium was used as a model pollutant to optimize two parameters of the assay: exposure periods (24, 96, 144 h) and salinity (0%, 25%, 50%, 75%, 100% sea water). Results revealed that salinity at or below 25% sea water at an exposure period of 144 h are the preferable conditions for detecting MT mRNA levels for in vitro assays employed on water samples from highly polluted brackish habitats.
Trace Metal Concentrations in Sediments and Oysters of Botany Bay, NSW, Australia by D. R. Spooner; W. Maher; N. Otway (pp. 0092-0101).
Surfical sediment (< 63 µm) trace metal concentrations (Zn, Cu, Pd, Cd, As) were analyzed from seven sites in Botany Bay, NSW, Australia, to assess the extent of contamination from the surrounding urban areas. The northwest shoreline of Botany Bay contained high surfical sediment trace metal concentrations relative to the southern shoreline. Surfical sediment Pb concentrations (10–120 µg/g) were above the current ANZECC/ARMCANZ interim sediment guideline value (50 µg/g) for the protection of benthic ecosystems at the northwest sites. Cooks River was identified as a major source of trace metals. Oysters grown in Botany Bay have greater Zn, Cu, and Cd concentrations than two relatively pristine reference locations, Jervis Bay and Batemans Bay, indicating that the Botany Bay region has elevated biologically available metal concentrations. Oyster tissue trace metal concentrations were below the Australian and New Zealand Food Authority standards. Translocation of oysters to sites around the bay identified Pb and Cd as the only trace metals to be accumulated over 3 months. Copper concentrations in transplanted oysters declined at most sites, indicating that the sites investigated in this study have less bioavailable copper than Woolooware Bay, the source of the oysters. The shallow waters along the southern shoreline are protected from the tidal flow that carry contaminated sediments and the biologically available trace metals appear to be low.
Bioconcentration of Cadmium and Toxic Effects on Life-History Traits of Pond Snails (Lymnaea palustris and Lymnaea stagnalis) in Laboratory Bioassays by M. Coeurdassier; A. De Vaufleury; P.-M. Badot (pp. 0102-0109).
We studied the bioconcentration and the individual effects of Cd on life-history traits of Lymnaea stagnalis and Lymnaea palustris exposed to increasing Cd concentrations for 4 weeks in controlled conditions. Internal Cd concentrations were linearly correlated to Cd concentrations of exposure in both foot and viscera of L. stagnalis and in the foot of L. palustris, and they were linked by a logistic relationship with environmental contamination in the viscera of L. palustris. If LC50s were higher than the highest Cd concentrations of exposure (L. stagnalis: 160 µg L–1; L. palustris: 320 µg L–1), other dose-dependent responses affecting life-history traits were noted in both species. In L. stagnalis, EC50 for growth was evaluated at 142 µg L–1 and growth inhibition was correlated with internal Cd concentrations by a linear relationship. L. palustris was more sensitive to Cd than L. stagnalis because its EC50-growth was three times lower (58 µg L–1 after 28 days). Dose-dependent responses were obtained for several parameters of fecundity of L. palustris. EC50 for the mean number of egg masses or mean number of eggs per individual were close to 60 µg L–1, whereas for the mean number of eggs per egg mass, the EC50 was higher, with a value of 124 µg L–1. The percentage of hatching versus the total number of eggs was 60% in controls, and no embryos were able to hatch at the lowest tested Cd concentration, 40 µg L–1. The high sensitivity of fertility was due to Cd blocking embryo development, particularly for the latest embryonic stages just before hatching. The present results constitute useful data to develop laboratory tests using pond snails for freshwater risk assessment.
Tissue-Specific HSP70 Levels and Reproductive Physiological Responses in Fishes Inhabiting a Metal-Contaminated Creek by J. L. Yoo; D. M. Janz (pp. 0110-0120).
The 70-kDa stress protein family (HSP70) plays important roles in a variety of physiological processes, including protein chaperoning, protection against apoptosis, steroidogenesis, and general cellular stress responses in vertebrate organisms, and has also been proposed as a biochemical marker of environmental stress, such as toxicant exposure. The objectives of this study were to determine HSP70 protein expression in head kidney, liver, gill, and ovarian tissues and to examine reproductive physiological responses in female fishes exposed chronically to sublethal metal concentrations. Female black bullhead (Ameiurus melas) and bluegill sunfish (Lepomis macrochirus) were collected from Tar Creek, Oklahoma (flowing through the Tri-State mining district) and from a nearby reference creek (Lytle Creek) during spring (prespawning; 26.5 ± 0.95°C water temperature) and winter (ovarian recrudescence; 4.8 ± 0.80°C water temperature). Aqueous (dissolved and suspended) concentrations of Cd and Zn and liver concentrations of Cd and Zn in both fish species were significantly greater at Tar Creek compared to Lytle Creek. HSP70 expression was consistently elevated in the head kidney of both fish species collected at Tar Creek in comparison to fish collected from the reference creek. In contrast, no consistent differences were observed in HSP70 expression in liver, gill, or ovarian tissues between sites. Significant seasonal differences were observed in expression of HSP70 in gill tissue of both species, in ovarian and liver tissue of bluegill sunfish and in head kidney of black bullhead. Serum testosterone concentration was significantly reduced in sunfish collected from Tar Creek during winter. Gonadosomatic and hepatosomatic indices were significantly lower in black bullhead collected from Tar Creek during spring, and condition factors were lower in black bullhead collected from Tar Creek during both spring and winter. There was no significant difference in the extent of ovarian follicular cell apoptosis in either species collected during spring. In conclusion, we observed significant tissue specific differences and seasonal variation in expression of HSP70, as well as alterations in circulating testosterone levels in female fish chronically exposed to metals.
Effects of Heavy Metal Exposure on Aggressive Behavior in a Small Territorial Songbird by E. Janssens; T. Dauwe; E. Van Duyse; J. Beernaert; R. Pinxten; M. Eens (pp. 0121-0127).
Several studies have shown that elevated levels of certain heavy metals may affect the behavior of birds and mammals. However, most of these studies were carried out under controlled laboratory conditions; results from free-living populations are scarce. In this study we examined the possible effects of exposure to high heavy metal concentrations on the aggressive behavior of resident great tit (Parus major) males by means of simulated territorial intrusion experiments during the egg-laying and incubation period at a highly polluted and a reference site. We also examined the effects of heavy metal exposure on the breeding performance of the tested couples, and we examined the plasma testosterone concentrations of great tit males in both study sites. We found no significant differences in the aggressive behavior between great tits at the polluted and the reference site during the egg-laying period. During the incubation period, responding male great tits at the polluted site performed significantly more aggressive flights around the decoy than did males at the reference site. During this period, there was also a tendency that more responding males were out of sight of the observer for some time during the experiment at the reference site than at the polluted site and this also for a longer period of time. Other behavioral parameters did not differ significantly between the two sites. Although plasma testosterone levels were higher at the polluted site, they did not differ significantly between the two sites. The tested couples at the polluted site interrupted their laying sequence significantly more and hatching success was significantly reduced compared to the tested birds at the reference site. We found no significant difference in clutch size, the length of the laying interruptions, fledging success, and fledgling age between the two sites. Although our results showed only minor alterations in the territorial aggressive behavior of male great tits exposed to heavy metal pollution, these small changes may have an important influence on the breeding and survival of these birds.
Environmental Contaminants in Liver and Kidney of Free-Ranging Northern Goshawks (Accipiter gentilis) from Three Regions of Germany by N. Kenntner; O. Krone; R. Altenkamp; F. Tataruch (pp. 0128-0135).
The northern goshawk (Accipiter gentilis) is a top predator in the terrestrial food web of large parts of the Holarctic. Due to its sedentary nature and well-investigated feeding ecology, it represents the most suitable bird of prey species in continental Europe for monitoring environmental pollutants. We analyzed the levels of organochlorine pesticides, polychlorinated biphenyls (PCB), and nonessential heavy metals in organ samples of 62 free-ranging northern goshawks found dead or injured in Germany from 1995 to 2001. Our results indicate significant differences in the contaminant burden of northern goshawks between three regions in Germany. Presumably, these differences were caused by different application periods and legislative restrictions before the German reunion, especially for the use of DDT in agriculture and forestry. Extraordinarily high residues of PCBs and DDE, the main metabolite of DDT, were found mainly in livers of northern goshawks inhabiting Berlin. Body condition is highly negatively correlated with the contamination level of the individual, especially for the persistent and lipophilic organochlorines and for mercury. PCB concentrations in hepatic tissue increase rapidly with age, and birds in their first summer had significantly lower levels than birds in their first winter or older. Adult female northern goshawks from Berlin had significantly higher hepatic concentrations of most of the higher-chlorinated PCBs and of cadmium than males from the same region. Cadmium residues were in general higher in renal tissue than in hepatic tissue, and cadmium levels in kidneys increased with age. Lead concentrations indicative of acute lead poisoning were detected in one bird and suggested in two others. All other heavy metal concentrations were low and represent background levels for birds of prey in Germany.
Polychlorinated Biphenyl (PCB) Congener Concentrations in Seabirds Found Dead in Mortality Incidents Around the British Coast by H. M. Malcolm; D. Osborn; J. Wright; C. L. Wienburg; T. H. Sparks (pp. 0136-0147).
Livers from 121 birds killed in mortality incidents in U.K. coastal waters between 1991 and 1996 were analyzed for 16 PCB congeners (IUPAC numbers 8, 18, 28, 31, 52, 77, 101, 118, 126, 128, 138, 149, 153, 169, 170, and 180). Species analyzed were guillemot (Uria aalge), shag (Phalacrocorax arisotelis), kittiwake (Rissa tridactyla), puffin (Fratercula arctica), razorbill (Alca torda), fulmar (Fulmarus glacialis), gannet (Sula bassana), and herring gull (Larus argentatus). This is the first report of PCBs in U.K. seabird tissues to be presented since 1983. Mean concentrations of total PCBs ranged from 0.47 to 15.8 mg/kg WW, similar to concentrations reported for North Sea birds during the 1970s and 1980s and lower than those reported for the same species in the Irish Sea during the late 1960s and early 1970s. The congeners generally present in the highest concentrations were (in decreasing order) 153, 138, 180, 118, and 170. Despite the birds having similar diets, both inter- and intraspecies differences in PCB congener profile were found. In guillemots from several sites on the east coast, the dominant congener was 138, compared to guillemots from the south coast, which had the more typical congener pattern found in seabirds. Some of the differences in total PCB values could be due to different causes of death, with a subsequent effect on body lipid levels.