Bioavailability of Arsenic and Antimony in Terrestrial Ecosystems: A Review

Arsenic (As) and antimony (Sb) are metalloids that belong to group 15 of the periodic table and exhibit toxic properties in the environment. They mostly occur naturally at low concentrations in soil, although these can be significantly elevated in both aquatic and terrestrial food chains as a result of dispersion from anthropogenic sources, e.g., mining activities. The bioavailability, i.e., the proportion of the contaminant in soil and dust that is available for uptake by plants and other living organisms, presents the greatest risk to terrestrial ecosystems. Various in vivo and in vitro methods have been used to measure As and Sb bioaccessibility in soil and dust. In vivo measurement of bioavailability can be time consuming, expensive, and unethical; thus, in vitro methods are commonly preferred. However, there is considerable uncertainty around the efficacy of in vitro tools used to measure the bioavailable fractions of As and Sb. The results of these methods are dependent on many variables, e.g., soil characteristics, contaminant sources, and chemical composition of in vitro methods. Therefore, substantial variations are observed between in vitro and in vivo results obtained from different test animals and endpoints. In this paper, we review the literature on As and Sb bioavailability in terrestrial ecosystems and current in vivo and in vitro techniques used for assessing bioavailability and bioaccessibility of metalloids. This would reveal research gaps and allow scientists and environmental policy makers to gain a deeper understanding of the potential risks associated with these metalloids in the environment.     

The effect of geographical variation of planting rate on the uptake of carbon by new forests of Great Britain

The planting rates from 1921 to 1996 of new coniferous and broadleavedforests for 11 regions of Great Britain were assembled for thestate and private sectors. Over that period new planting totalled231 kha of conifers and 132 kha of broadleaves in England, 141kha of conifers and 16 kha of broadleaves in Wales and 881 khaof conifers and 52 kha of broadleaves in Scotland. These time series and regional values of Yield Class were usedas input data for an accounting model of carbon in the trees,litter, soils and products to produce estimates of their netuptake of carbon by the forests from the atmosphere (i.e. increasein the carbon pools). On the assumption that conifer and broadleafplanting could be represented by Sitka spruce and beech treesrespectively, litter and forest soil in Great Britain were accumulatingcarbon at 2.42 Mt a^–1 in 1995–96. Coniferous forestaccounted for 89 per cent of this uptake. Scottish conifer andbroadleaf forests took up 68 per cent and mapping the uptakeshowed that the greatest rate occurred in western Scotland.The pool of carbon in wood products increased in 1995–96by 0.31 Mt a_–1. The estimated uptake rates were sensitive to the relative amountsof conifer and broadleaf forest planted (particularly in relationto increases in the pool of carbon in wood products) but notto regional differences in Yield Class. Use of any single YieldClass in the range 10–16 m³ ha^–1 a^–1 for allSitka spruce planting produced estimates of uptake rate in GreatBritain to trees, litter and soil within ±10 per centof that, assuming yield varied across the country. Lack of preciseknowledge on the parameters of the model was estimated to introducean uncertainty of ±30–70 per cent into estimatesof carbon uptake.     

Cardiac changes in experimental hyperthyroidism in dogs

Injection of triiodothyronine (T3) (1 mg/kg per day subcutaneously for 14 days) to 10 healthy dogs produced a hyperthyroid state characterised by high serum T3 concentrations, hypokalaemia, hyperactivity, loss of weight, diarrhoea and thirst. Electrocardiographic measurements showed that these dogs had an increase in heart rate of 63 +/- 11 beats/min with a significantly increased T wave amplitude without changes in R wave amplitude. Echocardiographic measurements showed no changes in fractional shortening and no evidence of ventricular hypertrophy, in contrast to reports in humans, cats and rats. However, the smooth muscle of the coronary arteries was markedly hypertrophied, which may cause a decrease in myocardial perfusion.     

Effects of 0.05% Chlorhexidine Lavage on the Tarsocrural Joints of Horses

In six horses, a 0.05% solution of chlorhexidine diacetate was used to lavage one tarsocrural joint; the contralateral control joint was lavaged with lactated Ringer's solution. Horses were evaluated daily for lameness. Synovial fluid samples were collected on days 1, 4, and 8 for determination of protein concentration, total and differential leukocyte counts, and mucin clot formation. After death on day 8, synovium and osteochondral samples were collected from the tarsocrural joints for examination of morphology and proteoglycan staining. Lavage with chlorhexidine solution caused lameness that was reduced but still evident at day 8. Synovial protein concentration was significantly increased by chlorhexidine lavage; the greatest increase occurred on day 1. Joint lavage increased synovial leukocyte counts on day 1, primarily by increasing polymorphonuclear (PMN) cell counts. Although total synovial leukocyte counts returned to normal by day 4, PMN cell counts remained elevated through day 8; PMN cell counts for chlorhexidine-lavaged joints were typically twice that of control joints. Chlorhexidine lavage caused synovial ulceration, inflammation, and abundant fibrin accumulation. Consistent differences in proteoglycan staining were not detected between control and chlorhexidine-lavaged joints. Joint lavage with 0.05% chlorhexidine diacetate, the lowest known bactericidal concentration, is not recommended for equine joints.     

Perianal Fistulas in the Dog Retrospective Evaluation of Surgical Treatment by Deroofing and Fulguration

Deroofing and fulguration (DR&F) was used as a surgical treatment for perianal fistulas in 30 dogs over a 5 year period at the University of Florida Veterinary Medical Teaching Hospital. A retrospective evaluation of the efficacy of this procedure was based on a written questionnaire completed by the owners. Dogs were placed initially into one of four categories according to their degree of perianal involvement: 0 to 90°, 91 to 180°, 181 to 270°, and 271 to 360°. The mean elapsed time between the last surgical treatment and follow-up evaluation was 39 months (range 6 to 63 months). Seventy-seven percent of the dogs were German shepherds. Sixty-seven percent of the dogs were intact males. The mean age of the dogs at the time of onset was 59 months (range 22 to 106 months). The most common presenting clinical signs were owner recognition of fistulous tracts (97%), tenesmus (37%), and licking of the perianal region (20%). The most frequently encountered postoperative complications were recurrence (70%) followed by varying degrees of incontinence (23%) and tenesmus (20%). Incontinence was transient in 5 of 7 dogs. Long-term results were the following: 5 dogs (17%) excellent, 13 dogs (43%) good, 3 dogs (10%) fair, and 9 dogs (30%) poor. Anal sacculectomy as an adjunct therapy was generally done only when the anal sacs were secondarily involved. In 2 dogs, prophylactic anal sacculectomy was done at the time of DR&F. The use of this technique is advocated in dogs moderately affected with perianal fistulas (0 to 180°) because of the minimal invasiveness, limited postoperative morbidity, and relative effectiveness of the procedure as demonstrated by the results of this study. In those dogs more severely affected, DR&F was not shown to be superior to other methods previously described.     

Success Rates of Unilateral vs. Bilateral Cataract Extraction in Dogs

Postoperative results of 113 unilateral and 77 bilateral extracapsular cataract extractions (EC-CEs) in dogs were evaluated retrospectively. Restoration or improvement of functional vision was achieved in 79.6% of the eyes in dogs with unilateral extraction and 85.7% of the eyes in dogs with bilateral extractions at weeks 4 to 6. Complications occurring 6 weeks to 9 months after lens extraction lessened the surgical success rate in both groups. Twenty-six percent of the dogs in which bilateral lens removal was performed suffered complications resulting in surgical failure in one eye. When using the criterion that one or both treated eyes had functional vision, a short-term success rate of 98.7% was found for bilateral extractions.     

Effects of Perioperative Granulocyte Colony-Stimulating Factor on Horses With Ascending Colonic Ischemia

Granulocyte colony-stimulating factor (G-CSF) is a glycoprotein that regulates the proliferation and maturation of hematopoietic progenitor cells and modulates the function of mature neu-trophils. The responses to administration of G-CSF alone, and in combination with antimicrobials, were studied in an equine model of ascending colon ischemia. Complete segmental colonic ischemia (3.75 hours) with pelvic flexure enterotomy was created in four treatment groups. Group 1 horses received recombinant canine G-CSF (10 μg/kg, every 24 hours, intramuscularly), gentamicin sulfate (2.2 mg/kg, every 8 hours, intravenously), and potassium penicillin G (40,000 lU/kg, every 6 hours, intravenously). Group 2 horses were treated with the G-CSF vehicle and antimicrobials as for group 1. Group 3 horses received G-CSF and the antimicrobial drug vehicles, and group 4 horses served as the untreated control receiving G-CSF vehicle and antimicrobial vehicles. The results for 20 horses, five horses in each group, were compared. Treatment with G-CSF was associated with an increased concentration of white blood cells, band neutrophils, neutrophils, lymphocytes, and monocytes in the peripheral blood after surgery. Antimicrobial administration had no detectable effect on cell concentrations after surgery. Administration of G-CSF was associated with an increased concentration of nucleated cells in the peritoneal fluid including neutrophils, small mononuclear cells and large mononuclear cells. Horses that developed incisional infections had lower neutrophil concentrations in the peripheral blood on postoperative day 2 than horses without infected incisions. These results suggested that the prophylactic administration of G-CSF may be useful in the treatment of patients at risk for developing neutropenia after surgery.     

Ceftiofur hydrochloride: plasma and tissue distribution in swine following intramuscular administration at various doses

Twelve mixed-breed swine (26.5-42.5 kg) received three daily intramuscular (i.m.) doses of ¹⁴C-ceftiofur hydrochloride. Three males and three females, received 6.76 ± 0.83 mg of ¹⁴C-ceftiofur free acid equivalents (CFAE)/kg body weight (b.w.)/day, while the other group received 4.41 ± 0.97 mg-CFAE/kg b.w./day. The swine were slaughtered 12 h following the last dose. Total dose accountability for the 6.76 mg dose was 91.44 ± 16.11% (72.51% in urine; 12.63% in faeces). For the 4.41 mg dose, accountability was 100.35 ± 20.45% (82.48% in urine; 12.85% in faeces). Within the tissues used for residue monitoring, the highest concentrations were observed in the kidneys (10.68 and 6.33 μg-CFAE/g for the 6.76 and 4.41 mg doses, respectively), followed by the injection sites, lungs, liver and muscle. In a separate study, twelve mixbreed swine (23.1-39.7 kg) received ¹⁴C-ceftiofur hydrochloride at 3.08 mg-CFAE/kg b.w. once daily for 3 days. Two males and two females were slaughtered at either 12, 72 or 120 h after the last dose. Total dose accountability for the 3.08 mg dose was > 83% (> 68% in urine; > 13% in faeces). In swine slaughtered 12 h after the last dose, residue concentrations closest to the safe concentrations were observed in the kidneys (3.62 μg-CFAE/ g), followed by the injection sites, lungs, liver and muscle.