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M S McLachlan

Publications and source records attributed to M S McLachlan.

At least 19 recordsLinked to original sources
PubMed2007

The influence of soil contamination on the concentrations of PCBs in milk in Siberia.

Although atmospheric deposition is generally the dominant pathway of PCBs into agricultural food chains, soil ingestion by livestock can be important in some cases. The relationship between PCB levels in cow's milk and in pasture soil was studied in the Irkutsk region in Siberia where an historical atmospheric source(s) of PCBs has led to widespread contamination of soil. Milk samples were collected in spring and again in autumn from 18 different farms and analyzed for PCBs. Pasture soil samples were also collected and analyzed. The PCB concentrations in both milk and soil ranged over more than an order of magnitude between the farms. A good correlation was obtained between PCB levels in autumn milk and in soil. This together with a range of other evidence suggested that ingestion of pasture soil was the dominant source of the PCB contamination in the milk. The average soil ingestion rate was estimated to be 1700 g/d, which is at the upper end of values reported in the literature. This may be due to the arid summer climate or the animal husbandry practices in Siberia.

Animal Husbandry↗
PubMed2005

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.

Journal Article↗
PubMed2001

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.

Algorithms↗
PubMed2001

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.

Adult↗
PubMed2001

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.

Absorption↗
PubMed2001

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.

Animal Feed↗
PubMed2000

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.

Air Pollution↗
PubMed1999

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.

Benzofurans↗
PubMed1999

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.

Adipose Tissue↗
PubMed1999

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.

Adult↗
PubMed1999

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.

Adipose Tissue↗
PubMed1998

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.

Adult↗
PubMed1997

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.

Animals↗
PubMed1995

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.

England↗
PubMed1994

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.

Journal Article↗
PubMed1993

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.

Adult↗
PubMed1983

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.

Abscess↗