Bioconcentration of persistent organic pollutants in four species of marine phytoplankton

The uptake of polychlorinated biphenyls (PCBs) was studied in four species of marine algae. A novel experimental system to establish and maintain constant dissolved concentrations of PCBs was employed. Headspace sampling was used to verify that the freely dissolved concentrations remained constant with time. The headspace analysis also allowed sorption to dissolved organic carbon (DOC) to be quantified for all but the most lipophilic PCB congeners. Equilibration with the dissolved phase was rapid for three of the four algae species (<1 d for the majority of congeners). Organic carbon-normalized algae/water partition coefficients (KAlgW) were similar for three of the four species, but were lower by a factor of 10 to 20 for Phaeodactylum tricornutum. The KAlgW values of the first three species were similar to the octanol/water partition coefficient (Kow) for those PCB congeners for which DOC sorption could be quantified. These KAlgW values also agreed well with organic carbon-normalized bioconcentration factors for PCBs in suspended particulate matter (BCF(SPM)) sampled in Baltic Sea surface water during the summer.

Observations of the PCB distribution within and in-between ice, snow, ice-rafted debris, ice-interstitial water, and seawater in the Barents Sea marginal ice zone and the North Pole area

To evaluate the two hypotheses of locally elevated exposure of persistent organic pollutants (POPs) in ice-associated microenvironments and ice as a key carrier for long-range transport of POPs to the Arctic marginal ice zone (MIZ), dissolved and particulate polychlorinated biphenyls (PCBs) were analyzed in ice, snow, ice-interstitial water (IIW), seawater in the melt layer underlying the ice, and in ice-rafted sediment (IRS) from the Barents Sea MIZ to the high Arctic in the summer of 2001. Ultra-clean sampling equipment and protocols were specially developed for this expedition, including construction of a permanent clean room facility and a stainless steel seawater intake system on the I/B ODEN as well as two mobile 370 l ice-melting systems. Similar concentrations were found in several ice-associated compartments. For instance, the concentration of one of the most abundant congeners, PCB 52, was typically on the order of 0.1-0.3 pg l(-1) in the dissolved (melted) phase of the ice, snow, IIW, and underlying seawater while its particulate organic-carbon (POC) normalized concentrations were around 1-3 ng gPOC(-1) in the ice, snow, IIW, and IRS. The solid-water distribution of PCBs in ice was well correlated with and predictable from K(ow) (ice log K(oc)-log K(ow) regressions: p<0.05, r2=0.78-0.98, n=9), indicating near-equilibrium partitioning of PCBs within each local ice system. These results do generally not evidence the existence of physical microenvironments with locally elevated POP exposures. However, there were some indications that the ice-associated system had harbored local environments with higher exposure levels earlier/before the melting/vegetative season, as a few samples had PCB concentrations elevated by factors of 5-10 relative to the typical values, and the elevated levels were predominantly found at the station where melting had putatively progressed the least. The very low PCB concentrations and absence of any significant concentration gradients, both in-between different matrices and over the Eurasian Arctic basin scale, suggest that ice is not an important long-range transport purveyor of POPs to the Arctic MIZ ecosystem.

Intestinal absorption and biomagnification of organic contaminants in fish, wildlife, and humans

Methods for the regulatory assessment of the bioaccumulation potential of organic chemicals are founded on empirical measurements and mechanistic models of dietary absorption and biomagnification. This study includes a review of the current state of knowledge regarding mechanisms and models of intestinal absorption and biomagnification of organic chemicals in organisms of aquatic and terrestrial food chains and also includes a discussion of the implications of these models for assessing the bioaccumulation potential of organic chemicals. Four mechanistic models, including biomass conversion, digestion or gastrointestinal magnification, micelle-mediated diffusion, and fat-flush diffusion, are evaluated. The models contain many similarities and represent an evolution in understanding of chemical bioaccumulation processes. An important difference between the biomagnification models is whether intestinal absorption of an ingested contaminant occurs solely via passive molecular diffusion through serial resistances or via facilitated diffusion that incorporates an additional advective transport mechanism in parallel (i.e., molecular ferrying within gastrointestinal micelles). This difference has an effect on the selection of physicochemical properties that best anticipate the bioaccumulative potential of commercial chemicals in aquatic and terrestrial food chains. Current regulatory initiatives utilizing Kow threshold criteria to assess chemical bioaccumulation potential are shown to be unable to identify certain bioaccumulative substances in air-breathing animals. We urge further research on dietary absorption and biomagnification of organic chemicals to develop better models for assessing the bioaccumulative nature of organic chemicals.

A food chain model to predict the levels of lipophilic organic contaminants in humans

A fugacity-based, nonsteady state, mechanistic model called ACC-HUMAN was developed to describe bioaccumulation of lipophilic organic pollutants from air, water, and soil to humans. The physical environment was linked via a marine and an agricultural food chain model to a human bioaccumulation model. Contaminant uptake via the primary dietary sources of persistent lipophilic contaminants in industrialized countries was addressed, namely fish, dairy products, and beef. In addition, uptake from air and water was considered, allowing the model also to treat less lipophilic compounds. To evaluate the model, the food chain characteristics were parameterized for southern Sweden and historical scenarios of polychlorinated biphenyl (PCB) concentrations in air, water, and soil in this region were constructed from published data. The resulting model predictions of PCB concentrations in fish, milk, beef, and human tissue agreed well with measured concentrations from Swedish monitoring programs. This suggests that ACC-HUMAN is a useful tool for predicting human exposure to bioaccumulative organic compounds. It can be linked easily to existing multimedia fate and transport models.

Stir bar contamination: a method to establish and maintain constant water concentrations of poorly water-soluble chemicals in bioconcentration experiments

A novel experimental system to establish and maintain constant dissolved concentrations of poorly water-soluble compounds for bioconcentration experiments with algae was developed. Although still recommended in the literature as a "non-adsorptive" material, a commercially available Teflon stir bar that was preloaded with polychlorinated biphenyls (PCBs) proved to be an effective donor for partitioning controlled delivery. When placed in a bioconcentration test chamber, the PCB concentrations in water and in the headspace remained constant for up to 8 days. Henry's law constants determined in experiments using water only were in good accordance with values found in the literature, indicating that the chemical was truly dissolved. When algae (Emiliana huxleyi, class prymnesiophyceae) were added to the chamber, the water and air concentrations varied initially but stabilised within several hours, and smooth uptake curves were obtained for the algae. This indicates that the contamination system compensates for chemical loss from the water column. In addition, the Henry's law constants and the headspace measurements were used to estimate what fraction of the PCB in filtered water was associated with dissolved organic carbon, opening the opportunity to constrain one of the major artefacts in bioconcentration experiments.

Bioaccumulation potential of persistent organic chemicals in humans

A model was used to explore the influence of physicalchemical properties on the potential of organic chemicals to bioaccumulate in humans. ACC-HUMAN, a model of organic chemical bioaccumulation through the agricultural and aquatic food chains to humans, was linked to a level I unit world model of chemical fate in the physical environment and parametrized for conditions in southern Sweden. Hypothetical, fully persistent chemicals with varying physical-chemical properties were distributed in the environment, and their bioaccumulation to humans was calculated. The results were evaluated using the environmental bioaccumulation potential (EBAP), defined as the quotient of the chemical quantity in a human divided by the quantity of chemical in the whole environment. Since the latter is closely related to emissions, EBAP is potentially a more useful tool for comparative risk assessment of chemicals than currently used medium-specific measures such as the fish-water bioaccumulation factor. A high environmental bioaccumulation potential, defined as > 10% of the maximum EBAP, was found for chemicals with 2 < log KOW < 11 and 6 < log KOA < 12. While these chemical partitioning properties clearly influenced bioaccumulation at each trophic level, these effects tended to equalize over the food web. The fact that the transfer from the environment as a whole to humans was quite uniform over a large chemical partitioning space suggests that these partitioning properties are relatively unimportant determinants of human exposure compared to other factors such as the substance's persistence in the environment and in the food web.

The influence of vertical sorbed phase transport on the fate of organic chemicals in surface soils

Gaseous exchange between surface soil and the atmosphere is an important process in the environmental fate of many chemicals. It was hypothesized that this process is influenced by vertical transport of chemicals sorbed to soil particles. Vertical sorbed phase transport in surface soils occurs by many processes such as bioturbation, cryoturbation, and erosion into cracks formed by soil drying. The solution of the advection/diffusion equation proposed by Jury et al. to describe organic chemical fate in a uniformly contaminated surface soil was modified to include vertical sorbed phase transport This process was modeled using a sorbed phase diffusion coefficient, the value of which was derived from soil carbon mass balances in the literature. The effective diffusivity of the chemical in a typical soil was greater in the modified model than in the model without sorbed phase transport for compounds with log K(OW) > 2 and log K(OA) > 6. Within this chemical partitioning space, the rate of volatilization from the surface soil was larger in the modified model than in the original model by up to a factor of 65. The volatilization rate was insensitive to the value of the sorbed phase diffusion coefficient throughout much of this chemical partitioning space, indicating that the surface soil layer was essentially well-mixed and that the mass transfer coefficient was determined by diffusion through the atmospheric boundary layer only. When this process was included in a non-steady-state regional multimedia chemical fate model running with a generic emissions scenario to air, the predicted soil concentrations increased by upto a factor of 25,whilethe air concentrations decreased by as much as a factor of approximately 3. Vertical sorbed phase transport in the soil thus has a major impact on predicted air and soil concentrations, the state of equilibrium, and the direction and magnitude of the chemical flux between air and soil. It is a key process influencing the environmental fate of persistent organic pollutants (POPs).

Modeling digestive tract absorption and desorption of lipophilic organic contaminants in humans

A model of the absorption and desorption of persistent lipophilic organic pollutants in the human gastrointestinal tract was formulated. The influence of the dietary intake of chemical, the chemical concentration in human tissue, the physical-chemical properties of the chemical, and the sorption properties of the feces on the predicted net mass transfer of chemical was explored and shown to be consistent with experimental observations. The model was parametrized and tested using a data set of approximately 800 measurements of net absorption/excretion of polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans that were obtained in experiments with 14 human volunteers. Overall good agreement was obtained between the predicted and measured values. The largest discrepancies were observed in cases of net excretion because the model was not able to account for the considerable individual and temporal variability in the sorption properties of the feces. In a sample model application, good agreement was found between concentrations of octachlorodibenzo-p-dioxin in blood measured in different age groups of the background population and values predicted by the model.

Seasonal variation of polychlorinated biphenyl concentrations in the southern part of the Baltic Sea

The impact of seasonal fluctuations in forcing factors such as atmospheric concentration, temperature, and biological productivity on the concentration of polychlorinated biphenyls (PCBs) in the surface water of the southern part of the Baltic Sea was investigated. Water samples were collected on eight cruises over 2 years. A clear seasonal variability in dissolved PCB concentrations was observed with higher levels in summer than in winter and spring. This was attributed to changes in atmospheric concentrations and water temperature, based on measurements showing the PCB levels in the atmosphere and surface water to be close to a partitioning equilibrium. Concentrations in the suspended particulate material (SPM) fraction were also variable, and when the quotient of the organic carbon normalised concentration in SPM and the dissolved concentration was calculated (i.e., the bioaccumulation factor (BAF)), a seasonal pattern was observed which was consistent with kinetic limitations on partitioning into particles caused by plankton growth. However, seasonal variability in the partitioning properties of the SPM may also contribute to this variability.

Partitioning of polychlorinated biphenyls and hexachlorobenzene into human faeces

The dietary absorption of persistent lipophilic organic pollutants (PLOPs) in humans is believed to occur via partitioning of the chemical between the lumen and the wall of the digestive tract. As such, the partitioning properties of the lumen contents are a key factor governing absorption. In this study, the partitioning properties of faeces were measured for 11 polychlorinated biphenyls and hexachlorobenzene (HCB). Four volunteers participated in the study, each of them providing faeces from a normal diet and a vegetarian diet. The faeces/gas equilibrium partition coefficient K(FG) varied by over three orders of magnitude between the different compounds. A linear relationship between log K(FG) and log KOA, the octanol/air partition coefficient, was observed. The slope of the relationship was > 1, indicating that the solvent properties of faeces were less polar than those of octanol. For a given compound, KFG varied up to a factor of 2.8 between the individuals on a normal diet. The influence of the vegetarian diet on K(FG) was negligible for the two volunteers who simply deleted fish and animal products from their normal diet, but K(FG) increased on average by a factor of 2 in the two individuals who increased their consumption of less readily digestible whole grains and vegetables in their vegetarian diet. On the basis of K(FG), the fugacities in the faeces were calculated. They were found to be much lower than the fugacities in blood. It is hypothesised that this is due to a temporary decrease in the fugacity in the wall of the jejunum caused by absorption of dietary lipids that results in equilibration between the lumen contents and the wall of the digestive tract at a fugacity below that present in the blood and the rest of the body.

Uptake and transfer of PCDD/Fs by cattle fed naturally contaminated feedstuffs and feed contaminated as a result of sewage sludge application. 2. Nonlactating cows

The dietary absorption and tissue distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) was investigated in 4 nonlactating Simmental cows. During Phase 1 the dietary uptake and fecal excretion of these chemicals were measured over 10 days using feed containing background levels of PCDD/Fs that were primarily of atmospheric origin. Following this, two of the animals were sacrificed and samples of different fat, muscle, and organ tissues were collected. In Phase 2 the remaining two animals were fed grass silage from a field which had a history of repeated sewage sludge applications. During the last 10 days of the 27-day feeding period, the dietary uptake and fecal excretion of PCDD/Fs were again quantified, after which these two animals were also sacrificed and sampled. The dietary absorption of the PCDD/Fs in the nonlactating cows agreed well with values reported in Part I of this series for lactating cows. In the two animals sacrificed at the end of Phase 1 that were close to a contaminant steady state, the lipid-normalized concentrations were similar in almost all tissues. The exceptions were the liver, and to a lesser extent the lungs and the spleen, which had higher levels; and the degree of elevation increased with the degree of chlorination of the PCDD/Fs. During Phase 2, the animals' body burden of several of the PCDD/F congeners increased markedly. The tissue analyses indicated that the chemicals were initially sequestered primarily in the liver, from where they were redistributed to the other tissues and organs. The rate of redistribution was related to the perfusion of the organ/tissue and decreased in the order lung>spleen>kidney>muscle>fat tissue. The rate of redistribution also decreased with increasing degree of chlorination of the PCDD/F congeners. Whereas virtually all of the 1,2,3,7,8-Cl(5)DD taken up during Phase 2 had been deposited in fat tissue by the end of the 27-day feeding period, three-quarters of the Cl(8)DD was still in the liver.

Uptake and transfer of PCDD/Fs by cattle fed naturally contaminated feedstuffs and feed contaminated as a result of sewage sludge application. 2. Nonlactating cows

The dietary absorption and tissue distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) was investigated in 4 nonlactating Simmental cows. During Phase 1 the dietary uptake and fecal excretion of these chemicals were measured over 10 days using feed containing background levels of PCDD/Fs that were primarily of atmospheric origin. Following this, two of the animals were sacrificed and samples of different fat, muscle, and organ tissues were collected. In Phase 2 the remaining two animals were fed grass silage from a field which had a history of repeated sewage sludge applications. During the last 10 days of the 27-day feeding period, the dietary uptake and fecal excretion of PCDD/Fs were again quantified, after which these two animals were also sacrificed and sampled. The dietary absorption of the PCDD/Fs in the nonlactating cows agreed well with values reported in Part I of this series for lactating cows. In the two animals sacrificed at the end of Phase 1 that were close to a contaminant steady state, the lipid-normalized concentrations were similar in almost all tissues. The exceptions were the liver, and to a lesser extent the lungs and the spleen, which had higher levels; and the degree of elevation increased with the degree of chlorination of the PCDD/Fs. During Phase 2, the animals' body burden of several of the PCDD/F congeners increased markedly. The tissue analyses indicated that the chemicals were initially sequestered primarily in the liver, from where they were redistributed to the other tissues and organs. The rate of redistribution was related to the perfusion of the organ/tissue and decreased in the order lung>spleen>kidney>muscle>fat tissue. The rate of redistribution also decreased with increasing degree of chlorination of the PCDD/F congeners. Whereas virtually all of the 1,2,3,7,8-Cl(5)DD taken up during Phase 2 had been deposited in fat tissue by the end of the 27-day feeding period, three-quarters of the Cl(8)DD was still in the liver.

Partitioning of polycyclic aromatic hydrocarbons in the polyethylene/water system

The suitability of polyethylene sheets as passive samplers of lipophilic contaminants in water bodies was tested. High-density polyethylene (HDPE) and low-density polyethylene (LDPE) sheets were contaminated with PAH. Uncontaminated and pre-contaminated sheets were deployed simultaneously and collected at intervals over 32 days. The exposed sheets and water samples were analyzed for PAH. The initial PAH concentrations in the contaminated and uncontaminated sheets differed by two to three orders of magnitude, but approached a common equilibrium concentration during exposure. The two- to four-ring PAH achieved quasi-equilibrium within the 32-day exposure period, whereas the five- and six-ring PAH did not. The estimated PE/water partition coefficients were approximately three times higher for HDPE than for LDPE, and they were similar in magnitude to the K(ow) values (the partition coefficients between n-octanol and water). The uptake rate constants were approximately four times higher for HDPE than LDPE, which was attributed to the four times higher specific surface area. The uptake and elimination in HDPE followed linear first-order kinetics, whereas for LDPE very slow elimination rates were observed that could not be explained. The results show that PE is a simple, effective, and inexpensive material for sampling trace organic contaminants in water.

The influence of dietary concentration on the absorption and excretion of persistent lipophilic organic pollutants in the human intestinal tract

The gastrointestinal exchange of polychlorinated biphenyls (PCBs), dibenzo-p-dioxins, and dibenzofurans (PCDD/Fs) as well as hexachlorobenzene was measured in five volunteers. The dietary intake and the fecal excretion of the chemicals were quantified and the net absorption/net excretion was calculated as the difference between these two fluxes. Experiments were conducted using an elevated dietary intake and a reduced dietary intake of chemical, and the results were compared with the absorption during normal dietary intake. The net absorption varied widely with the dietary intake for those compounds which bioaccumulate in humans; high dietary intake of chemical resulted in absorption approaching 100% of intake, while low dietary intake resulted in a net excretion several times greater than the dietary intake. In contrast to net absorption, the chemical flux in the feces was largely independent of the dietary intake of chemical for a given individual. Good agreement was found between the feces/blood distribution coefficients measured in this study and in a study with contaminated workers whose blood concentrations were several orders of magnitude higher, indicating that fecal excretion of chemical is linearly proportional to the blood concentration. The results suggest that gastrointestinal exchange can be viewed as two processes operating simultaneously: absorption of contaminant from the diet, and excretion of contaminant from the body's reservoirs via the feces. By subtracting that component of the fecal flux originating from the body, the maximum dietary absorption could be calculated. This was >95% for most of the compounds, decreasing to a minimum of 50-60% for the octachlorinated dioxins and furans. The maximum dietary absorption showed a Kow dependency consistent with the two film model of gastrointestinal absorption of persistent organic chemicals.

PAHs, PCDD/Fs, PCBs and HCB in leaves from Brisbane, Australia

The concentrations of SOCs in leaves of an evergreen Australian native tree (Melaleuca leucadendra) and grass collected in Brisbane, Australia were determined. The concentrations of PCDD/Fs and PAHs in the leaf tissue were comparable to those reported for urbanised areas in other industrialised countries. A distinct difference in the compound profiles between the leaves of the two species was observed, with higher concentrations of the lower molecular mass PAHs and PCDD/Fs and lower concentrations of the higher molecular mass PAHs and PCDD/Fs in the Melaleuca leaves relative to the grass leaves. The interspecies differences are explained on the basis of the larger size of the lipophilic compartment (for compounds with low K(OA)) and the lower ratio of surface area to volume in the Melaleuca leaves.

PCDDs in the water/sediment-seagrass-dugong (Dugong dugon) food chain on the Great Barrier Reef (Australia)

Polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) concentrations were measured in sediment and seagrass from five locations in or adjacent to the Great Barrier Reef Marine Park. A full spectrum of Cl5-8DDs were present in all samples and, in particular, elevated levels of Cl8DD were found. PCDFs could not be quantified in any samples. The PCDD concentrations ranged over two orders of magnitude between sites, and there was a good correlation between sediment and seagrass levels. There were large quantities of sediment present on the seagrass (20-62% on a dry wt. basis), and it was concluded that this was a primary source of the PCDDs in the seagrass samples. The PCDD levels in the seagrass samples were compared with the levels in the tissue of three dugongs stranded in the same region. The relative accumulation of the 2,3,7,8-substituted PCDD congeners in the dugongs decreased by over two orders of magnitude with increasing degree of chlorination. This was attributed to the reduced absorption of the higher chlorinated congeners in the digestive tract, a behaviour that has been observed in other mammals such as domestic cows.

Retention and mobility of atmospheric particle-associated organic pollutant PCDD/Fs and PAHs in maize leaves

The fate of polychlorinated dibenzo-p-dioxins and dibenzofurans and polycyclic aromatic hydrocarbons deposited to maize leaves under ambient conditions was investigated, with focus on those compounds that are primarily associated with particles in the atmosphere. Leaf samples collected from mature maize plants over an 8-wk period were subjected to four extraction procedures: (1) rinsing with distilled water; (2) shaking in aqueous EDTA solution; (3) immersion in chloroform/methanol; (4) soxhlet extraction with toluene. Of the compounds deposited primarily in association with particles, > 20% of the total leaf contamination was present in the first two aqueous extracts, indicating that only a small portion of these substances was subject to ready erosion from the leaf surfaces. Some 50-60% of the chemical was present in the third extract, while 20-40% was found in the final extract. The chemical in the final extract was no longer associated with particles, since these had been removed with the first three extractions. This chemical must have desorbed from the particles with which it was originally deposited, and migrated through the epicuticular waxes. Model calculations indicated that 15-35% of the chemical in the third extract had also desorbed from the particles, and there was evidence that polychlorinated dibenzo-p-dioxins and dibenzofurans desorb more readily than polycyclic aromatic hydrocarbons. It is concluded that desorption of chemical from particles and subsequent transport through the cuticle is an important process determining plant accumulation of organic contaminants associated with atmospheric particles.

The kinetics and reversibility of the partitioning of polychlorinated biphenyls between air and ryegrass

Lolium multiflorum (ryegrass) was contaminated with technical mixtures of polychlorinated biphenyls (PCBs) via the gas phase and the subsequent elimination of the PCBs from the vegetation was studied under field conditions. There was a pronounced decrease in the concentrations of the di- through to the pentachlorinated congeners over the 240-h elimination period. For many of the congeners the elimination was nearly complete, suggesting that the partitioning of these compounds from the gas phase into ryegrass is largely reversible. The elimination followed first order kinetics. The elimination half-lives were linearly proportional to the plant/air equilibrium partition coefficients (K(PA)) of the PCB congeners and ranged from 22 h for PCBs 8 + 5 to 87 h for PCBs 84 + 101. For the hexa- through to the octachlorinated congeners no significant decrease in the concentration of the vegetation was observed during the elimination experiment. The elimination was described well using a two-resistance model of PCB desorption which indicated that elimination of the di- and trichlorinated PCBs was limited by transport within the plant itself while elimination of the higher chlorinated congeners was limited by transport from the plant surface into the atmosphere. Furthermore, the results demonstrate that if elimination of higher chlorinated PCBs from ryegrass via biological or photochemical degradation occurs, then it is very slow.

A non-absorbable dietary fat substitute enhances elimination of persistent lipophilic contaminants in humans

For individuals contaminated with persistent lipophilic pollutants, there is an urgent need for a therapy to enhance contaminant elimination from the body and hence reduce long term exposure. This study investigated the possibility of enhancing the excretion of native chemical via the faeces by augmenting the lipophilic properties of the faeces with the non-absorbable lipid substitute olestra. The faecal excretion of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and hexachlorobenzene (HCB) was measured in 3 volunteers. The excretion while eating an olestra-free diet was compared with the excretion while eating a diet supplemented wit 25 g/d of olestra. The excretion while on the olestra diet was higher by a factor of 1.5-11, depending on the compound. This resulted from higher concentrations of the contaminants in the faeces and higher excretion of faeces dry mass due to the food additive. Using 2,3,7,8-Cl4DD as an example, it was estimated that ingestion of 25 g/d of olestra would more than double the overall rate of elimination of this compound from the body. It is concluded that regular consumption of olestra may provide a therapeutic approach for reducing the body burden of persistent lipophilic contaminants.

Clearance of PCDD/Fs via the gastrointestinal tract in occupationally exposed persons

A digestive tract mass balance was performed on six men with high body burdens of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Intake via food was measured by analyzing duplicate portions of the food consumed by the volunteers and excretion via feces was determined by quantitative collection and analysis of the feces. Blood samples were taken to determine the current body burden. The results showed that the quantity of non-metabolized chemical excreted in the feces clearly exceeded the uptake via food for all of the 2,3,7,8-substituted PCDDs and some of the PCDFs, indicating a significant clearance across the gastrointestinal tract. The concentrations of these PCDD/F congeners in blood and feces were highly correlated (r > 0.8), demonstrating that the fecal PCDD/F content was determined by the body burden. The half lives in the test persons due to fecal clearance of non-metabolized chemical were estimated from the excretion rate and the current body burden and ranged between 10 years (Cl8DD) and 33 years (2,3,4,7,8-Cl5DF). These were compared with the overall contaminant half-lives due to all clearance processes which were calculated from the body burden and the decrease in blood concentrations measured over several years. The fecal clearance of non-metabolized PCDD/F contributed on average between 37% (2,3,7,8-Cl4DD) and 90% (Cl8DD) to the total elimination. This indicates that the gastrointestinal pathway plays a decisive role in the clearance of most 2,3,7,8-subsituted PCDD/F congeners.

Polychlorinated dibenzo-p-dioxins and dibenzofurans in Great Barrier Reef (Australia) dugongs (Dugong dugon)

Fat tissue samples from dugong (Dugong dugon) carcasses stranded at three sites along the Great Barrier Reef were analysed for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). Relatively high levels of PCDDs were determined in all three dugongs. In particular OCDD, the PCDD/F congener that is usually considered the least bioavailable of all 2,3,7,8 substituted congeners, was found at levels higher than reported for other marine mammals. Tissue accumulation of PCDDs by dugongs may be a consequence of sediment and/or seagrass ingestion during feeding, microbial biotransformation of PCDD precursors in the animal's hindgut or, alternatively, the possession of a selective degradation capability for PCDFs.

PCDD/Fs in textiles--part II: transfer from clothing to human skin

The transfer of PCDD/Fs from contaminated textiles to the outermost layers of the skin (stratum corneum) of human volunteers was measured. The experiments were conducted with cotton T-shirts containing high levels of hepta- and octachlorinated dibenzo-p-dioxins and dibenzofurans. The results indicated that there is little spatial variability in the transfer from the T-shirt to the skin surface (< factor2) and also little variability among individuals (< factor 3). The percent transfer from different cotton textiles (sigma PCDD/F: 1,900 pg/g - 281,000 pg/g) to the stratum corneum was found to be similar. The transfer from a white, unbleached polyester material was more than an order of magnitude lower, indicating that the PCDD/Fs were more tightly bound to the polyester than to the cotton. It was shown that the PCDD/Fs penetrate into deeper layers of the stratum corneum during an 8 hour exposure period. However, systemic exposure and a significant contribution of this pathway to the PCDD/F body burden is only possible if the compounds are able to overcome the penetration barrier posed by the viable epidermis.

Digestive tract absorption of PCDD/Fs, PCBs, and HCB in humans: mass balances and mechanistic considerations

Gastrointestinal absorption of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs) and hexachlorobenzene (HCB) from food was investigated in seven individuals aged 24 to 81 years with different contaminant body burdens using a mass balance approach. The difference between the ingested and excreted amounts of the chlorinated compounds was defined as net absorption. No analyzed compound was absorbed completely, and some were excreted to a greater extent than ingested, resulting in a net excretion. The absorption behavior was predominantly controlled by blood lipid levels: good correlations were obtained between the net absorption and the lipid-based concentrations in the blood for almost all of the persistent compounds studied. Expressed in international toxicity equivalents (I-TEq), the maximum absorption of PCDD/Fs among the volunteers was 63% and, for the three oldest volunteers, a net excretion of I-TEq was found. The high absorption levels of many compounds could not be explained on the basis of diffusive gradients estimated from the difference between the lipid-based food and blood concentrations; the diffusive gradient was consistently negative. Adding a factor to account for the reduction in the lipid content of the food during passage through the digestive tract did not resolve this problem. To explain this discrepancy, a "fat-flush" theory was postulated, which hypothesizes that the fat compartment of the absorbing tissue expands due to the uptake of dietary fat, resulting in a decrease of this compartment's lipid-based concentrations below the food's, hence facilitating absorption. The fat-flush hypothesis provides a theoretical basis for a two-step model of organic pollutant transfer in the gastrointestinal tract, with absorption and excretion as distinct processes occurring at different locations.

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in Baikal seal

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were determined in blubber tissue of one 3 month and two adult female seals from Lake Baikal. High PCDD and PCDF concentrations were found in the Baikal seal. The levels are comparable with those reported for ringed seals (phoca hispida) living in the Baltic sea, and Barrow Strait and Admiralty Inlet in the Canadian Arctic.

PCDD/Fs and non-o-PCBs in digested U.K. sewage sludges

Twelve digested sewage sludges from rural and urban waste water treatment works in the north-west of England were analysed for PCDD/Fs and non-o-PCBs. The PCDD/F analysis of eight samples was repeated using high-resolution mass spectrometry, which enabled detection of the lower chlorinated congeners and calculation of TE values. sigma TEQ values for these eight samples ranged from 19-206 ng/kg with the higher values detected in the samples from urban/industrial areas. Examination of the congener/homologue profiles for the more contaminated samples suggests a major input from the use of pentachlorophenol. Archived sewage sludge samples collected and stored from one sewage treatment works in the south of England between 1942 and 1960 were analyzed to gain some insight into temporal trends and possible variations in source inputs. These provide some evidence of changing sources of PCDD/Fs over time and a decline in sigma TEQs since the 1950s.

Textiles as a source of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in human skin and sewage sludge

Polychlorinated dibenzo-p-dioxins and dibenzofurans were measured in low- to high-ppb concentrations in several pieces of new clothing from different manufacturers. It was shown that these contaminants are transferred from textiles to human skin during wearing. They were also present in shower water and were washed out of textiles during washing. Extensive evidence was found indicating that contaminated textiles are a major source of chlorinated dioxins and furans in non-industrial sewage sludge, dry cleaning residues and house dust.

A study of the influence of sewage sludge fertilization on the concentrations of PCDD/F and PCB in soil and milk

The influence of the agricultural use of sewage sludge on the concentrations of PCBs and PCDD/Fs in soil, feed and milk was investigated on four dairy farms. Evidence of contaminant accumulation in the soil was found on both farms that fertilized with sewage sludge. The concentrations in feed and milk from one of these farms were similar to the concentrations in the matched control, while the concentrations in the samples from the second sludge user were elevated. The study demonstrates that the agricultural use of sewage sludge does under some conditions lead to higher levels of PCBs and PCDD/Fs in food products.

Digestive tract absorption of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in a nursing infant

The digestive tract absorption of environmental contaminants is an important but poorly understood parameter in contaminant is an important but poorly understood parameter in contaminant risk assessments. The net absorption of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in a nursing infant was measured under natural conditions over 12 days. The levels of the substances in the mother's milk were typical for Germany. It was found that for almost all congeners over 90% of the ingested compound was absorbed. This indicates that the common assumption of 100% absorption in nursing infants is reasonable. No firm conclusions could be drawn regarding the absorption of Cl7- and Cl8DD/F due to high blank levels in the cotton diapers used.

Urachal abnormalities in the adult

A spectrum of rare urachal abnormalities in the adult is described, including urachal cyst, infected urachal cyst and abscess, and urachal carcinoma. The clinical and radiographic features are presented, and diagnosis using ultrasound, computed tomography, and needle aspiration is discussed. Treatment of infected urachal cysts with percutaneous catheter drainage is described.

1-Alpha-hydroxy vitamin D in dialysis bone disease: radiological changes after 6 and 12 months of treatment

Biochemical, radiological and histological indicators of dialysis bone disease were studied before, 6 months (58 patients) and 12 months (48 patients) after starting treatment with 1 alpha-OH D3. Radiographic healing of subperiosteal erosions was seen after 6 months in 60% and after 12 months in 77% of affected patients. Radiographic improvement, however, was not significantly related to reductions in resorptive surfaces seen on quantitative bone histology, nor to changes in plasma concentrations of immunoreactive parathyroid hormone. Metastatic calcification appeared or increased in 43% of patients after 6 months and 52% after 12 months. Periosteal new bone developed or increased in 14% of patients after 6 months and 17% after 12 months. Both metastatic calcification and periosteal new bone formation were associated with high plasma phosphate concentrations, but not with plasma calcium, alkaline phosphatase or parathyroid hormone concentrations. Treatment with 1 alpha-OH D3 produces radiological improvement in the majority of patients with dialysis bone disease, but the lack of correlation with histological changes confirms the need for regular radiographic examination. Metastatic calcification and periosteal new bone formation probably represent toxicity of 1 alpha-OH D3 but may be minimised by phosphate restriction.

Percutaneous antegrade extrusion of ureteral stones

A technique to extrude small obstructing ureteral stones with a catheter through a percutaneous nephrostomy tract is described. The technique was successfully used to extrude obstructing ureteral stones in three patients who had ileal loop urinary diversions and who were poor operative risks, and in one patient who had had no previous urinary tract surgery. In these four patients, ureteral stones were dislodged and removed without complication. The technique may have advantages over previously described techniques, particularly in patients with ileal conduits in whom established retrograde cystoscopic techniques are difficult to perform, and in patients who are poor operative risks.

Observer variation in lower limb venography

Three radiologists examined 34 venograms (68 limbs) performed supine without fluoroscopy for evidence of thrombosis. At 11 major veins in each limb they stated whether thrombus was "absent," "doubtful," "presumed" or "definite" or expressed " "no opinion." Data were analyzed by using the kappa statistic, which corrects for chance agreement. Results were compared with those from a previous study in which two of the observers assessed venograms performed under fluoroscopic control with the patient semi-erect. In the present study observers expressed "no opinion" much more often, particularly for anterior tibial and iliac veins. With these examinations excluded, the extent of observer variation was similar in the two studies, disagreement about the presence of thrombus occurring in about 10% of examinations. The frequency with which the diagnosis of thrombus remains in doubt severely limits the value of venography performed supine without fluoroscopy. Fluoroscopically-controlled examinations in the semi-erect position are preferable.

Aging and simple cysts of the kidney

Abdominal CT scans of 103 patients without evidence of renal disease were examined. Unsuspected simple renal cysts were demonstrated in 25 (24%). No cysts were demonstrated in patients less than 40 years old. Thereafter the number of cysts and the number of patients with cysts tended to increase with age. Cyst dimensions also increased. These observations suggest that the development of simple cysts of the kidney is related to aging.

Observer variation in the interpretation of lower limb venograms

After agreeing on diagnostic criteria and after a pilot study, two experienced radiologists twice independently reviewed 40 lower limb venograms performed by a standard technique in patients suspected or known to have venous thrombosis. The observers reviewed 20 examinations at a time, their analysis requiring separate identification of 11 major veins. At each site observers stated whether thrombus was "absent," "doubtful," "presumed," or "definite," or declared "no opinion possible." They then rediscussed criteria of diagnosis and, using the same experimental design, examined another 40 venograms. To correct for agreement expected by chance, data were analyzed by using the kappa statistic. In general, levels of agreement were higher than those reported for many other clinical and radiologic investigations, probably because of refinement of criteria after the pilot study. Nonetheless, observers disagreed about the probable presence or absence of thrombus at some site in the limb in about 10% of examinations. Observer variation should be considered when venography is used as a reference standard to evaluate other methods of diagnosing thrombi.

Observer variation in interpreting radiographs of the pituitary fossa

Observer variation in interpreting sellar radiographs in patients suspected or known to have a pituitary tumor has been examined. Two radiologists experienced in interpreting sellar radiographs examined independently, without clinical details, plain films and tomograms of the sella of 101 patients. In most, only minor changes were anticipated. Of the 93 female patients, 67 were under investigation for amenorrhea. Radiographs were examined four times, each radiologist examining each set twice. Appearances were classified as normal, doubtful or abnormal on each occasion. Overall intraobserver agreement was 76%--85%. Neither radiologist changes his opinion by more than one category, e.g. from normal to doubtful. Overall interobserver agreement was 63%--75%. Disagreement between observers concerning 11 (11%) of the patients resulted from differences of opinion about whether minor changes in sellar outline represented an abnormality or merely a normal variation. Kappa analysis suggested that much of the agreement may be ascribed to chance. Agreement rates resemble those for other clinical and radiological investigations.

The effect of radiology electives on career choice at McMaster University

Recruitment ot radiology is said to be affected by the extent to which radiologists participate in medical student teaching. At McMaster University, where radiologists make major contributions to the medical school curriculum, students appear to show little interest in radiology as a career. The characteristics, attitudes and career choices of students at McMaster who undertook elective periods in radiology between 1973 and 1976 were examined. Though students rated the elective experience very highly, none intended to become a radiologist. Half of the group wished to take up family practice, the proportion in the school as a whole being similar. This is consistent with policies of student selection and education at McMaster. Most of those choosing family practice did not change their career choice between entry to and exit from the school. Involvement of radiologists in the curriculum had no detectable positive influence on career choice.

Uterine cirsoid aneurysm

Cirsoid (or varicose) aneurysm of the uterine vessels causes severe, life-threatening uterine bleeding. Previous trophoblastic neoplasia is a common predisposing factor. Diagnosis is by arteriography and may be missed without it.

Effect of oophorectomy and calcium deprivation on bone mass in the rat

1. The effects of a low calcium diet and of oophorectomy, separately and together, on cortical and trabecular bone mass, have been examined in mature female rats. 2. Calcium deprivation caused a significant decrease of weight, cortical cross-sectional area and ratio of cortical to total area in the femur, it significantly reduced the volume of trabecular bone and increased the percentage of osteoid surface in the tail vertebrae, and in addition increased the urinary excretion of phosphate and, initially, of hydroxyproline. 3. Oophorectomy caused similar though smaller changes in trabecular bone and urine, whereas the effects of oophorectomy on cortical bone were greater on a low calcium intake than on a normal intake. 4. The ash weight of the femora, expressed as a percentage of the total dry weight, was unaffected by calcium deprivation or oophorectomy alone but was significantly reduced when the two occurred together. 5. The percentage of resorption surfaces in the vertebrae tended to increase on the low calcium diet and after oophorectomy on the normal diet but decreased after oophorectomy on a low calcium diet. 6. It is concluded that oophorectomy and calcium deficiency each reduce bone mass in the adult rat but the greatest effect is seen when they are combined.

Failure to prostaglandin A1 to modify renal diatrizoate uptake in experimental acute renal failure

Acute renal failure (ARF) was induced in rats by intramuscular injection of glycerol. Forty-eight hours later prostaglandin A1 (PGA1) in a dose of 1, 5 or 25 microgram/kg bodyweight or phosphate buffer was infused intravenously over 15 min into these animals and controls. After 14 min, 125I-labeled diatrizoate was injected intravenously in a dose of 15 mg/kg bodyweight. Uptake and distribution of diatrizoate were measured one minute later in whole kidneys or kidney slices to provide indices of glomerular filtration. Diatrizoate concentrations were also measured in liver, plasma and washed red cells. Plasma volume was estimated with 125I-labeled albumin. PGA1 produced a dose-related increase in plasma diatrizoate concentration in ARF which was not accounted for by changes in uptake by the kidney, liver or red cells or by changes in plasma volume. It exceeded the relatively small increase in diatrizoate uptake which occurred in the kidney. Intrarenal distribution of diatrizoate did not change. These observations in the kidney suggest that intravenous PGA1 does not improve glomerular filtration in this model of established ARF.

Bone mass measurement using a xenon-filled multiwire proportional counter as detector

The application of a xenon-filled multiwire proportional counter to photon absorptiometry of bone mass is described. Performance characteristics obtained from a prototype system are discussed and future developments indicated.

Tumoral calcinosis: a manifestation of extreme metastatic calcification occurring with 1, alpha-hydroxycholecalciferol therapy

Two cases are reviewed, both of which developed tumoral calcinosis whilst receiving 1, alpha-hydroxy-cholecalciferol therapy. Tumoral calcinosis is an extreme form of peri-articular calcification, and its occurrence in patients with chronic renal failure is unusual. These peri-articular masses developed around the shoulders in both patients, and the action of 1, alpha-hydroxycholecalciferol as a possible factor promoting this form of metastatic calcification is discussed.