A Bayesian approach to assessing the uncertainty in estimating bioconcentration factors in earthworms--the example of quinoxyfen

BACKGROUND: Quinoxyfen is a fungicide of the phenoxyquinoline class used to control powdery mildew, Uncinula necator (Schw.) Burr. Owing to its high persistence and strong sorption in soil, it could represent a risk for soil organisms if they are exposed at ecologically relevant concentrations. The objective of this paper is to predict the bioconcentration factors (BCFs) of quinoxyfen in earthworms, selected as a representative soil organism, and to assess the uncertainty in the estimation of this parameter. Three fields in each of four vineyards in southern and northern Italy were sampled over two successive years. RESULTS: The measured BCFs varied over time, possibly owing to seasonal changes and the consequent changes in behaviour and ecology of earthworms. Quinoxyfen did not accumulate in soil, as the mean soil concentrations at the end of the 2 year monitoring period ranged from 9.16 to 16.0 µg kg^?1 dw for the Verona province and from 23.9 to 37.5 µg kg^?1 dw for the Taranto province, with up to eight applications per season. To assess the uncertainty of the BCF in earthworms, a probabilistic approach was used, firstly by building with weighted bootstrapping techniques a generic probabilistic density function (PDF) accounting for variability and incompleteness of knowledge. The generic PDF was then used to derive prior distribution functions, which, by application of Bayes' theorem, were updated with the new measurements and a posterior distribution was finally created. CONCLUSION: The study is a good example of probabilistic risk assessment. The means of mean and SD posterior estimates of log BCFworm (2.06, 0.91) are the ‘best estimate values’. Further risk assessment of quinoxyfen and other phenoxyquinoline fungicides and realistic representative scenarios for modelling exercises required for future authorization and post‐authorization requirements can now use this value as input. Copyright © 2011 Society of Chemical Industry     

Mast cell tumour and cutaneous histiocytoma excision wound healing in general practice

Objective : To assess whether wounds from incomplete mast cell tumour excisions are at greater risk of healing complications than wounds from complete excisions, or cutaneous histiocytomas. Methods : Mast cell tumours and cutaneous histiocytomas submitted to Nationwide Laboratories between November 1, 2007 and April 30, 2008 were selected. Questionnaires were sent to submitting veterinarians requesting details of tumour characteristics, clinical approach to the tumour and wound healing. Results : Three hundred and eighty‐six mast cell tumours and 524 cutaneous histiocytomas were identified. One hundred and eighty‐five mast cell tumours and 244 cutaneous histiocytomas questionnaires were returned (47% response). Wound complications arose in 20% of mast cell tumours and 21% of cutaneous histiocytomas. Multivariable analysis confirmed that larger tumours, tumours on the feet and a soft/“baggy” appearance, were significantly associated with a greater frequency of problems, leading to delayed wound healing and dehiscence. Clinical Significance : Incomplete mast cell tumour excision does not lead to greater risk of wound complications. Mast cell tumour surgical wounds have a similar rate of wound complications as cutaneous histiocytoma wounds.     

Does the Degree of Preoperative Subluxation or Soft Tissue Tension Affect the Incidence of Postoperative Luxation in Dogs after Total Hip Replacement?

Objective: To investigate whether preexisting coxofemoral subluxation/luxation predisposes to postoperative total hip replacement (THR) luxation. Study Design: Case series. Animals: Dogs (n=100) that had cemented THR (n=109); 23 normal controls. Methods: A preliminary study was performed to validate our methods of assessing luxation and laxity by comparing dogs with severe hip dysplasia with a control population of normal dogs. For the main study, the records and radiographs of all dogs that had primary THR were reviewed. Measurements taken from preoperative radiographs to quantify hip subluxation/laxity included the Norberg angle, subluxation index, and 2 new measures: acetabular depth ratio (ADR) and dorsal acetabular rim ratio (DARR). Differences between groups that had luxation within 8 weeks and those that did not were investigated. Results: Postoperative luxation occurred in 13 dogs (12%) within 8 weeks of surgery. Luxation was significantly associated with various measurements (including Norberg angle, ADR, DARR) thought to reflect degree of subluxation/soft tissue tension. Conclusion: Luxation after canine THR is a multifactorial problem but preexisting subluxation/soft tissue laxity is a significant risk factor for this complication.     

Recent advances in the management of bovine tuberculosis in free-ranging wildlife

Established foci of Mycobacterium bovis (the causative agent of bovine tuberculosis [bTB]) in free-ranging wildlife are currently under various stages of management on three continents (Africa, Europe and North America) and in New Zealand. Other, as yet undiagnosed, foci seem likely to exist elsewhere. The complex roles that these wildlife foci play in the ecology of bTB remain among the greatest challenges facing bTB control globally. Conceptually, management of bTB in free-ranging wildlife can be thought of as progressing from the discovery of an outbreak through frequently overlapping stages of epidemiological characterization, initial control, simulation and forecasting, focused control, and verification of eradication. Surveillance in its various forms remains a critical component of assessment throughout. Since the Fourth International M. bovis Conference in 2005, research on management of bTB in free-ranging wildlife has encompassed such areas as the human dimensions of wildlife management, mitigation of bTB risks from wildlife on cattle farms, vaccine biology, and epidemiology, with a major contribution from simulation modeling. In order to advance the actual field management of bTB, however, research must be sufficiently grounded to aid development of practical, affordable and politically defensible management interventions which stand a reasonable chance of being implemented. The current management of two wildlife reservoirs of bTB, brushtail possums (Trichosurus vulpecula) in New Zealand, and white-tailed deer (Odocoileus virginianus) in Michigan, USA, serve as contrasting examples of different wildlife management strategies aimed at achieving a common goal. In New Zealand, the importance of agricultural export markets and the status of the possum as a non-native pest have facilitated direct, aggressive management of the disease reservoir, resulting in considerable progress towards bTB freedom since 1994. In Michigan, the relative importance of the hunting economy and of whitetails as a game animal have made such aggressive culling politically untenable. This has forced reliance upon publicly supported, and implemented, management tools, and so provided impetus to better understand social support for wildlife management policy, its limitations, and ways to employ it in disease control policy development.     

Silicon nutrition of rice is affected by soil pH,weathering and silicon fertilisation

Silicon (Si) is a beneficial element for tropical grasses such as rice (Oryza sativa) and responses to applications of Si are common on highly weathered soils. However, the importance of pH (and hence Si speciation), weathering and fertilisation on Si uptake is still poorly understood. The responses of rice to Si fertilisation were studied in two variably weathered basalt soils (Red Ferrosol, Grey Vertosol) adjusted at different pH values (5.5–9.5) with three levels of acidulated wollastonite. Soil Si was extracted using deionised water (H₂O), 0.01 M CaCl₂, or 0.5 M NH₄OAc. Significant increases in Si uptake and rice biomass were observed in the Red Ferrosol following fertilisation (p < 0.01). Greater biomass production was observed at lower pH, due to decreased Si sorption and higher solution Si concentrations. Silicon uptake by rice was greater at low pH, despite similar extractable Si concentrations; suggesting a relationship between Si speciation and uptake. In contrast, Si uptake and rice shoot dry matter in the less weathered Grey Vertosol were unaffected by Si fertilisation (p > 0.05) except at the highest rate and lowest pH (5.5). Solution Si concentrations were controlled by precipitation/polymerisation reactions in equilibrium with specific soil pH values rather than adsorption processes. Silicon speciation effects (monosilicic acid vs. silicate ions) were unable to be measured due to an induced phosphorus deficiency in both soils at pH values > 8.5. In conclusion, weathered soils are more responsive to Si fertilisation and Si uptake is increased at low pH.     

Modeling shallow water table evaporation in irrigated regions

Groundwater discharge through evaporation due to a shallow water table can be an important component of a regional scale water balance. Modeling this phenomenon in irrigated regions where soil moisture varies on short time scales is most accurately accomplished using variably saturated modeling codes. However, the computational demands of these models limit their application to field scale problems. The MODFLOW groundwater modeling code is applicable to regional scale problems and it has an evapotranspiration package that can be used to estimate this form of discharge, however, the use of time-invariant parameters in this module result in evaporation rates that are a function of water table depth only. This paper presents a calibration and validation of the previously developed MOD-HMS model code using lysimeter data. The model is then used to illustrate the dependence of bare soil evaporation rates on water table depth and soil moisture conditions. Finally, an approach for estimating the time varying parameters for the MODFLOW evapotranspiration package using a 1-D variably saturated MOD-HMS model is presented.     

Influence of permethrin droplets on movement of larval Plutella xylostella (Lepidoptera: Plutellidae)

The behavioral response of larvae of the diamondback moth (Plutella xylostella L.) to permethrin droplets was investigated through computer simulations and videotape analysis of larval movement on treated surfaces. Simulations of pre-contact avoidance responses and post-contact hypersensitivity responses indicated that the different response types would produce different effects on larval speeds and leaving times in the presence of insecticide. Analysis of actual larval movement in treated arenas demonstrated that responses to permethrin consistent with the predictions for pre-contact avoidance did occur. Larval speeds were higher in trials with insecticide droplets than in controls, and these differences arose prior to contact with droplets. When a higher insecticide concentration was used for droplets, the response observed was consistent with a relatively longer distance avoidance response than when droplets had lower permethrin concentrations. Such a response to permethrin should significantly decrease larval exposure to insecticides and increase survival in permethrintreated fields.