Failure of generic risk assessment model framework to predict groundwater pollution risk at hundreds of metal contaminated sites: Implications for research needs.

Soil pollution constitutes one of the major threats to public health, where spreading to groundwater is one of several critical aspects. In most internationally adopted frameworks for routine risk assessments of contaminated land, generic models and soil guideline values are cornerstones. In order to protect the groundwater at contaminated sites, a common practice worldwide today is to depart from health risk-based limit concentrations for groundwater, and use generic soil-to-groundwater spreading models to back-calculate corresponding equilibrium levels (concentration limits) in soil, which must not be exceeded at the site. This study presents an extensive survey of how actual soil and groundwater concentrations, compiled for all high-priority contaminated sites in Sweden, relate to the national model for risk management of contaminated sites, with focus on As, Cu, Pb and Zn. Results show that soil metal concentrations, as well as total amounts, constitute a poor basis for assessing groundwater contamination status. The evaluated model was essentially incapable of predicting groundwater contamination (i.e. concentrations above limit values) based on soil data, and erred on the "unsafe side" in a significant number of cases, with modelled correlations not being conservative enough. Further, the risk of groundwater contamination was almost entirely independent of industry type. In essence, since neither soil contaminant loads nor industry type is conclusive, there is a need for a supportive framework for assessing metal spreading to groundwater accounting for site-specific, geochemical conditions.

Metal solubility and transport at a contaminated landfill site - From the source zone into the groundwater.

Risks associated with metal contaminated sites are tightly linked to material leachability and contaminant mobility. In this study, metal solubility and transport were characterized within a glass waste landfill through i) lysimeter-collection of pore water and standardized batch leaching tests, ii) soil profiles extending from the landfill surface, through unsaturated soil underneath, and into the groundwater zone, and iii) groundwater samples upstream, at, and downstream of the landfill. The soil analyzes targeted both pseudo-total and geochemically active concentrations of contaminant metals (As, Cd, Pb, Sb) and basic soil geochemistry (pH, org. C, Fe, Mn). Water samples were analyzed for dissolved, colloid-bound and particulate metals, and speciation modelling of the aqueous phase was conducted. The results revealed a highly contaminated system, with mean metal concentrations in the waste zone between 90 and 250 times the regional background levels. Despite severe contamination of the waste zone and high geochemically active fractions (80-100%) of all contaminant metals as well as elevated concentrations in landfill pore water, the concentrations of Cd and Pb decrease abruptly at the transition between landfill and underlying natural soil and no indication of groundwater contamination was found. The efficient cation retention is likely due to the high pH. However, the sorption of As and Sb is weaker at such high pH, which explains their higher mobility from the pore water zone into groundwater. The field soil:solution partitioning (Kd) displayed a high spatial variability within the waste zone (the highest Kd variability was seen for Pb, ranging from 140 to 2,900,000 l kg-1), despite little variability in basic geochemical variables, which we suggest is due to waste material heterogeneity.

The risk of overestimating the risk-metal leaching to groundwater near contaminated glass waste deposits and exposure via drinking water.

This study investigates metal contamination patterns and exposure to Sb, As, Ba, Cd and Pb via intake of drinking water in a region in southeastern Sweden where the production of artistic glass has resulted in a large number of contaminated sites. Despite high total concentrations of metals in soil and groundwater at the glassworks sites properties, all drinking water samples from households with private wells, located at a 30-640m distance from a glassworks site, were below drinking water criteria from the WHO for Sb, As, Ba and Cd. A few drinking water samples showed concentrations of Pb above the WHO guideline, but As was the only element found in concentrations that could result in human exposure near toxicological reference values. An efficient retention of metals in the natural soil close to the source areas, which results in a moderate impact on local drinking water, is implied. Firstly, by the lack of significant difference in metal concentrations when comparing households located upstream and downstream of the main waste deposits, and secondly, by the lack of correlation between the metal concentration in drinking water and distance to the nearest glassworks site. However, elevated Pb and Cd concentrations in drinking water around glassworks sites when compared to regional groundwater indicate that diffuse contamination of the soils found outside the glassworks properties, and not only the glass waste landfills, may have a significant impact on groundwater quality. We further demonstrate that different mobilization patterns apply to different metals. Regarding the need to use reliable data to assess drinking water contamination and human exposure, we finally show that the conservative modelling approaches that are frequently used in routine risk assessments may result in exposure estimates many times higher than those based on measured concentrations in the drinking water that is actually being used for consumption.

Antimicrobial screening of zinc in the absence or presence of oleoresins and various resin acids.

Zinc and oleoresins are the main components of several wound dressings, and are also frequently used in root canal treatment. The in vitro antibacterial effects of zinc, six highly purified resin acids and two commercial oleoresins alone or combined in varying proportions were analysed. Oleoresins are composed of approximately 90% resin acids and the most common acids were included in this study. The antibacterial activity of the various chemicals was estimated using a Bioscreen robot analyser, which allowed 24 h kinetic documentation of bacterial growth. The bacteria employed were reference species commonly occurring on human skin or of oral origin. Zinc as well as the oleoresins and the pure resin acids all showed antibacterial activity when present in growth media, but the sensitivity of the bacteria varied. The presence of resin acids and oleoresins increased the antibacterial effect of zinc to varying degrees depending on the combination and the bacterial species tested. The results of the present study indicate that zinc, resin acids, or oleoresins alone, as well as combined, show antibacterial activity against selected aerobic Gram-positive and anaerobic Gram-negative bacteria.

The effect of zinc on bacterial phagocytosis, killing and cytoprotection in human polymorphonuclear leucocytes.

An in vitro study examining the effects of zinc treatment on human PMN cell phagocytosis and killing of Staphylococcus aureus and Staphylococcus epidermidis and the cytoprotection of zinc against staphylococcal toxins. Phagocytosis was studied by transmission electron microscopy using different microbiological techniques, one of which was designed to follow the kinetics of bacterial killing. No effect was found on phagocytosis and bacterial killing. The cytotoxic effects of a crude toxin and an alpha-toxin extracted from Staphylococcus aureus preparations were studied on human PMN cells using the standard 51Cr release assay. Both toxins induced a dose-dependent leakage of 51Cr, indicating cell membrane damage. These results were confirmed by electron microscopy during the phagocytosis of S. aureus, where severe PMN cellular degeneration was observed. The addition of zinc to PMN cells strongly inhibited the release of 51Cr. In conclusion, our results show that zinc in higher than physiological concentrations does not inhibit PMN cell functions such as phagocytosis and intracellular killing of S. aureus and S. epidermidis. The addition of zinc may be beneficial in certain clinical situations, such as wound healing, zinc deficiency and infections involving toxin-producing bacteria, e.g. S. aureus.

Toxic effects of some conifer resin acids and tea tree oil on human epithelial and fibroblast cells.

The present study was undertaken to assess and compare the in vitro cytotoxic effects of three resin acid analogues: dehydrobietic acid, podocarpic acid, O-methylpodocarpic acid; an essential oil from Australia (tea tree oil); and tapped oleoresin from Thailand, on human epithelial and fibroblast cells, using a quantitative neutral red spectrophotometric assay. All of the investigated compounds except for tea tree oil exhibited a cytotoxic activity which was proportional to their concentrations and time of exposure up to 24 h, i.e. higher concentrations and longer time of exposure caused increased cell death. Dehydroabietic acid and the oleoresin were the most toxic compounds followed by O-methylpodocarpic acid, whereas podocarpic acid and tea tree oil showed a lower level of toxicity. On the basis on these findings it is concluded that an isopropyl group on the aromatic C-ring is of great importance for the cytotoxicity of the tested abietane resin acids, thus indicating that the cytotoxic activity of oleoresins most probably is caused by synergistic or additive effects of resin acids. The results from this work support the view that antibacterial activity parallels cytotoxic activity which suggests a similar mode of action, most probably exerted by membrane-associated reactions.

Bilateral chronic compartment syndrome in the forearm and the hand.

We report two cases of bilateral chronic exertional compartment syndrome (CCS) in the forearm and hand. Measurement of the intramuscular pressure was useful for diagnosis. These two cases illustrate that bilateral CCS should be suspected in patients complaining of bilateral exercise-induced pain in the anconeus muscle, the forearms, the thenar and hypothenar regions and in the first dorsal interosseous muscle. Fasciotomy relieved the pain in both cases.

Neutralizing effect of zinc oxide on dehydroabietic acid-induced toxicity on human polymorphonuclear leukocytes.

The cytotoxic effect of dehydroabietic acid (DHAA), a resin acid found in rosin, was studied on human polymorphonuclear leukocytes (PMN) using leakage of 51Cr from prelabeled cells, supravital staining, and transmission electron microscopy. DHAA caused a strong dose-related release of 51Cr, a high uptake of trypan blue, and total cell necrosis as seen in transmission electron microscopy. Albumin slightly reduced the toxic effects, whereas the addition of zinc in various forms strongly inhibited these toxic effects of DHAA in the concentration range 10-500 micrograms/mL. In the presence of albumin, zinc oxide as a suspension inhibited the damage of the cell membranes more than a filtrate of zinc oxide, indicating a subsequent slow release of zinc from the zinc oxide.

Neutralizing effect of zinc oxide on dehydroabietic acid-induced toxicity on human polymorphonuclear leukocytes.

The cytotoxic effect of dehydroabietic acid (DHAA), a resin acid found in rosin, was studied on human polymorphonuclear leukocytes using leakage of 51Cr from prelabeled cells, supravital staining, and transmission electron microscopy. DHAA caused a strong dose-related release of 51Cr, a high uptake of trypan blue, and total cell necrosis, as seen in transmission electron microscopy. Albumin slightly reduced the toxic effects, whereas the addition of zinc in various forms strongly inhibited these toxic effects of DHAA in the concentration range of 10-500 micrograms/mL. In the presence of albumin, zinc oxide as a suspension inhibited the damage of the cell membranes more than a filtrate of zinc oxide, indicating a subsequent slow release of zinc from the zinc oxide.

Antibacterial activity of rosin and resin acids in vitro.

The antibacterial effects of rosins and resin acids were studied in vitro using three methods, disc diffusion on agar, agar dilution, and broth dilution. Rosin and some resin acids had antibacterial effects that were restricted to Gram-positive bacteria. The abietic type of acids had a more pronounced antibacterial activity than the pimaric and labdane acids when the disc diffusion method was used but there was no inhibition of growth of Gram-negative bacteria. Among the individual resin acids, dehydroabietic acid was generally the most potent, when disc diffusion on agar was used, and prediffusion increased the inhibitory effect. The composition of the pure resin acids dehydroabietic, neoabietic, and isopimaric acid did not change during the experiment, but abietic and levopimaric acid were converted into dehydroabietic acid by the addition of Müller-Hinton agar. In conclusion the old tradition of treating wounds with pitch, sap, rosin, or rosin containing tapes might therefore have some antibacterial relevance.

Antibacterial effects of zinc oxide, rosin, and resin acids with special reference to their interactions.

The growth inhibiting capacity of zinc oxide combined with ordinary rosin (Portuguese rosin), abietic acid or dehydroabietic acid was studied using two different methods. To mimic the actual treatment of wounds, circular tapes or sensitivity discs were placed on Müller-Hinton-agar plates that had been seeded with various facultative aerobic bacteria, and the zones of inhibition were measured. The agar dilution method was used to measure the minimum inhibitory concentration (MIC). Inhibition of growth was restricted to Gram-positive facultative aerobic bacteria for the individual substances zinc oxide, Portuguese rosin, or resin acids, as well as for combinations of these. In general the combination of zinc oxide and dehydroabietic acid was a more potent antibacterial substance than the corresponding combination of zinc with rosin or abietic acid. These combinations commonly had synergistic antibacterial effects.

Antibacterial effect of zinc oxide in vitro.

Antibacterial activity, zinc concentrations and pH were measured in Müller-Hinton broth containing different amounts of zinc oxide and inoculated with Staphylococcus aureus (10(6) colony forming units/ml). The minimum inhibitory concentrations (MIC) of zinc oxide to different clinical isolates were determined using the Müller-Hinton agar dilution tests. Gram-positive bacteria were most susceptible. Gram-negative aerobic bacteria and streptococci were usually not inhibited even at the highest concentrations used (1024 micrograms/ml), but staphylococci--particularly some isolates of Staphylococcus epidermidis--were sensitive enough to allow determination of their MIC.

The effect of zinc oxide on Staphylococcus aureus and polymorphonuclear cells in a tissue cage model.

The effect of zinc oxide on S. aureus (209 P) was studied in steel net tissue cages implanted subcutaneously in guinea pigs and rabbits. Zinc oxide installed in the tissue cages created high, sustained concentrations of zinc in the cage fluid throughout the study. In a concentration of 22 mmol/l zinc oxide reduced viable counts in tissue cage fluid inoculated with S. aureus. No deleterious effect was observed on polymorphonuclear cell function.

The effects of occlusive dressings on inflammation and granulation tissue formation in excised wounds in rats.

The effects on the healing of full-thickness excisional wounds treated with either of two occlusive dressings (Mezinc or Duoderm) were compared with the effects of gauze soaked in saline. The wounds were made on 86 rats and were examined clinically, histologically and biochemically four, eight and twelve days after wounding. Four days postoperatively the Duoderm-treated wounds differed significantly from the other two groups. Clinically, an adherent discolored gelatinous mass remained after removal of the firm part of the Duoderm dressing. Histologically it corresponded to a superficial exudate containing polymorphonuclear leukocytes (PMNs), macrophages and condensed foreign material. There was also a more extensive inflammatory reaction in the underlying tissues compared with gauze or Mezinc treatment and debris was seen in vesicles extracellularly and in foamy macrophages. Foamy macrophages were only seen in the Duoderm-treated wounds. These macrophages were mainly confined to the granulation tissue, which was about twice as thick as in the other two treatment groups twelve days after excision.

The use of a water extract from the bark of Choerospondias axillaris in the treatment of second degree burns.

Burns are common in Vietnam, and because of economic constraints and limited resources for the import of appropriate treatments, the health authorities are obliged to rely on traditional herbal remedies. It is therefore essential to evaluate current drugs, one of which is the water extract of the bark of the tree Choerospondias axillaris. It has been used for many years in the Vietnam-Sweden hospital at Uong Bi in northern Vietnam. We assessed the efficacy of the remedy in an open, randomised controlled clinical trial, in which 20 patients with second degree burns were treated with the extract of the Choerospondias axillaris and 19 with saline gauze. The mean healing time was significantly shorter for patients treated with Choerospondias axillaris (11 days) compared with patients treated with saline gauze (17 days) (p < 0.01), and the number of wound infections was significantly lower in the Choerospondias axillaris group (7/20 compared with 16/19, p = 0.003). The bark extract was easy to apply and additional wound care was not usually necessary, while the treatment with saline gauze was laborious for both patients and staff and was much more expensive. The extract from Choerospondias axillaris is a convenient treatment for second degree burns in both children and adults.

Wound contraction and zinc absorption during treatment with zinc tape.

Wound healing, wound contraction and zinc absorption were studied in rats operated on with excisional wounds on each side of the dorsolateral aspects of the backs. The wounds were covered with plastic foil, plastic tape or zinc tape. The shortest healing time was seen in wounds treated with plastic foil when the contralateral wound was treated with zinc tape. Final wound contraction was decreased when the wound was treated with plastic-coated tape and zinc tape that was fixed to the surrounding skin. An increase in serum zinc concentration was seen 7 days postoperatively when the animals were treated with zinc tape and a decrease in serum zinc concentration was seen at the same time when only plastic foil was used.

Muscle strength is improved after parathyroidectomy in patients with primary hyperparathyroidism.

Fatigue and muscular weakness are prevalent symptoms in patients with primary hyperparathyroidism. This study examined muscular strength before and after operation in a group of eight patients with hyperparathyroidism and in a control group of seven patients with benign thyroid lesions. The maximum power grip, pronation and supination, and endurance for the same muscular movements, were studied by means of a computer program. Patients with hyperparathyroidism had impaired muscular strength compared with the controls but 12 months after operation a significant improvement of all muscular performance was observed. No such improvement was detectable among the controls. There was no correlation between the levels of serum calcium and parathyroid hormone and the measurements recorded before and after operation. Muscular impairment in hyperparathyroidism is measurable by an objective technique. Improvement occurs after surgery.

Treatment of keloids and hypertrophic scars with adhesive zinc tape.

A report is given on the treatment of keloids and hypertrophic scars using ordinary zinc tape. Among 41 patients who had their keloids or hypertrophic scars covered with zinc tape, the size of the scars in 23 patients was reduced to the level of the surrounding skin within the mean treatment time of 6 months. In the remaining patients the size of the keloids also decreased and treatment is being continued. The itching decreased in all the 37 patients who suffered from itching before tape treatment and in 20 patients it disappeared totally. The redness of the scars decreased in all cases.

Escherichia coli dimethylallyl diphosphate:tRNA dimethylallyltransferase: essential elements for recognition of tRNA substrates within the anticodon stem-loop.

Escherichia coli dimethylallyl diphosphate:tRNA dimethylallyltransferase (DMAPP-tRNA transferase) catalyzes the alkylation of the exocyclic amine of A37 by a dimethylallyl unit in tRNAs with an adenosine in the third anticodon position (position 36). By use of purified recombinant enzyme, steady- state kinetic studies were conducted with chemically synthesized RNA oligoribonucleotides to determine the essential elements within the tRNA anticodon stem-loop structure required for recognition by the enzyme. A 17-base oligoribonucleotide corresponding to the anticodon stem-loop of E. coli tRNA(Phe) formed a stem-loop minihelix (minihelix(Phe)) when annealed rapidly on ice, while the same molecule formed a duplex structure with a central loop when annealed slowly at higher concentrations. Both the minihelix and duplex structures gave k(cat)s similar to that for the normal substrate (full-length tRNA(Phe) unmodified at A37), although the K(m) for minihelix(Phe) was approximately 180-fold higher than full-length tRNA. The A36-A37-A38 motif, which is completely conserved in tRNAs modified by the enzyme, was found to be important for modification. Changing A36 to G in the minihelix resulted in a 260-fold reduction in k(cat) compared to minihelix(Phe) and a 13-fold increase in K(m). An A38G variant was modified with a 9-fold reduction in k(cat) and a 5-fold increase in K(m). A random coil 17-base oligoribonucleotide in which the loop sequence of E. coli tRNA(Phe) was preserved, but the 5 base pair helix stem was completely disrupted and showed no measurable activity, indicating that a helix-loop structure is essential for recognition. Finally, altering the identity of several base pairs in the helical stem did not have a major effect on catalytic efficiency, suggesting that the enzyme does not make base-specific contacts important for binding or catalysis in this region.