Prostate cancer risk and exposure to pesticides in British Columbia farmers.

BACKGROUND: Several epidemiologic studies have reported an increased risk of prostate cancer among farmers. Our aim was to assess the risk of developing prostate cancer in relation to exposure to specific active compounds in pesticides. METHOD: A case-control approach was used with 1,516 prostate cancer patients and 4,994 age-matched internal controls consisting of all other cancer sites excluding lung cancer and cancers of unknown primary site. Lifetime occupational history was obtained through a self-administered questionnaire and used in conjunction with a job exposure matrix to estimate the participants' lifetime cumulative exposure to approximately 180 active compounds in pesticides. Conditional logistic regression was used to assess prostate cancer risk, adjusting for potential confounding variables and effect modifiers. These include age, ethnicity, alcohol consumption, smoking, education, and proxy respondent. RESULTS AND CONCLUSIONS: The significant association between prostate cancer risk and exposure to DDT (OR = 1.68; 95% CI: 1.04-2.70 for high exposure), simazine (OR = 1.89; 95% CI: 1.08-3.33 for high exposure), and lindane (OR = 2.02; 95% CI: 1.15-3.55 for high exposure) is in keeping with those previously reported in the literature. We also observed a significant excess risk for several active ingredients that have not been previously reported in the literature such as dichlone, dinoseb amine, malathion, endosulfan, 2,4-D, 2,4-DB, and carbaryl. Some findings in our study were not consistent with those reported in the literature, including captan, dicamba, and diazinon. It is possible that these findings showed a real association and the inconsistencies reflected differences of characteristics between study populations.

Effect of hydration on interstitial distribution of charged albumin in rat dermis in vitro.

At physiological pH, negatively charged glycosaminoglycans in the extracellular matrix may influence distribution volume of macromolecular probes, a phenomenon of importance for hydration of the interstitium and therefore for body fluid balance. We hypothesized that such charge effect was dependent on hydration. Human serum albumin (HSA) (the pH value for the isoelectric point (pI) = 4.9) was made neutral by cationization (cHSA) (pI = 7.6). Rat dermis was studied in vitro in a specially designed equilibration cell allowing control of hydration. Using a buffer containing labelled native HSA and cHSA, the distribution volumes were calculated relative to that of 51Cr-EDTA, an extracellular tracer. During changes in hydration (H), defined as (wet weight - dry weight) (dry weight)(-1)), the slope of the equation describing the relationship between extracellular fluid volume (V(x)) (in g H2O (g dry weight)(-1)) and H (V(x) = 0.925 H + 0.105) differed significantly from that for available volumes of cHSA (V(a,cHSA) = 0.624 H - 0.538) and HSA (V(a,HSA) = 0.518 H - 0.518). A gradual reduction in H led to a reduction in difference between available volumes for the two albumin species. Screening the fixed charges by 1 m NaCl resulted in similar available and excluded volumes of native HSA and neutral cHSA. We conclude that during gradual dehydration, there is a reduced effect of fixed negative charges on interstitial exclusion of charged macromolecules. This effect may be explained by a reduced hydration domain surrounding tissue and probe macromolecules in conditions of increased electrostatic interactions. Furthermore, screening of negative charges suggested that hyaluronan associated with collagen may influence intrafibrillar volume of collagen and thereby available and excluded volume fraction.

A hierarchical approach to coding chemical, biological and pharmaceutical substances.

This hierarchical coding system is designed to classify substances into successively subordinate categories on the basis of chemical, physical and biological properties. Although initially developed for occupational cancer epidemiological studies, it is general in nature and can be used for other purposes where a systematic approach is needed to catalogue or analyze large numbers of substances and/or physical properties. The coding system incorporates a multi level approach, where substances can be coded both on the basis of function and composition. On the first level, a three digit code is assigned to each substance to indicate its primary use in the occupational environment (e.g. pesticide, catalyst, adhesive). Substances can then be coded using a ten digit code to indicate structure and composition (e.g. organic molecule, biomolecule, pharmaceutical). Depending on the complexity required, analysis can incorporate the three digit code, ten digit code, or a combination of both. The approach to coding both chemical and biological agents is modeled in part after conventional approaches used by the International Union of Pure and Applied Chemists (IUPAC) and the International Union of Biochemists (IUB). Development of the coding system was initiated in the 1980's in response to a need for a system allowing analysis of individual agents as well classes or groups of substances. The project was undertaken as a collaborative venture between the BC Cancer Agency, Cancer Control Research program (then Division of Epidemiology) and the Department of Chemical and Biological Engineering at the University of British Columbia.

Modeling of occupant-generated CO2 dynamics in naturally ventilated classrooms.

A numerical method is presented to estimate the concentration of occupant-generated CO(2) for the (time-varying) occupancy typically found in nonforced ventilated elementary school classrooms. Here, the governing mass balance was solved numerically and compared to experimental measurements in order to estimate the respiration and (time-varying) infiltration rates. For the cases studied, we estimate an average CO(2) generation rate per child as 404 mg/min(-1). This is similar to estimates found in the literature for the age and activity level of elementary students, the classroom occupants. The average estimated infiltration rates were found to be larger than those measured from the decay of the tracer gas SF(6) under closed-door static conditions. The in-use infiltration rates were increased by additional air exchange due to people entering and leaving the room. In addition, we show that the difference (or error) between the instantaneous concentration of CO(2) and the time-averaged value recorded by a data-logging CO(2) monitor varies depending on the infiltration rate and sampling time. Therefore, the time interval selected for averaging may increase the overall error of the apparent CO(2) concentration. We conclude that the methods used to measure air exchange rates in naturally ventilated rooms underestimate the actual ventilation rate of a room under "in-use" conditions. However, even with the addition of uncontrolled outdoor air, the concentration of CO(2) in the classrooms studied was higher than recommended to meet air quality objectives.

Simultaneous measurement of interstitial fluid pressure and load in rat skin after strain application in vitro.

Skin provides the flexible, protective covering of the body. It consists of a network of fibrous proteins embedded in a viscoelastic gel. Theoretical models of soft tissue demonstrate that behavior of such systems is strongly influenced by the relationship between the interstitial fluid pressure (P(if)) and solid matrix stress. A microtensiometer for loading skin uniaxially in vitro was, therefore, developed and used in conjunction with the established servo-null micropipette technique to measure P(if). Dorsal rat skin specimens were preloaded to 100 mN, where P(if) was 2.3 +/- 1.3 mmHg (mean +/- SE, n = 12) above ambient, and then strained by 4%. Load instantaneously increased and the subsequent decay was described by the function, F(t) = F(1)[1-C(f)Ln(t)]. F(1), related to the instantaneous elasticity, was 272 +/- 42 mN (n = 12) while, C(f) was 0.0894 +/- 0.0026 [Ln(s)](-1) (n = 12). A similar function P(t) = P(s)(1) x [1-C(ps)Ln(t)], where P(s)(1) = 27 +/- 5 mmHg and C(ps) = 0.1274 +/- 0.0097 [Ln(s)](-1) (n = 12) fitted the decay of P(if) after 20 s with a residual > or = 0.82, though, P(if) fell more rapidly over the initial 10 s. P(if) and stress can be measured simultaneously with the apparatus, though more precise determination of the depth at which pressure is measured is required for quantitative comparison of the magnitude of these two parameters.

Effect of charge on interstitial distribution of albumin in rat dermis in vitro.

At physiological pH, negatively charged glycosaminoglycans in the extracellular matrix may influence distribution volume of a probe. We hypothesized that by varying the probe charge we would be able to observe a graded response of available volume fraction. Human serum albumin (HSA) (isoelectric point (pI) 5.0) was made more positive by cationization. Using reaction times of 10, 45 and 60 min, cationized HSA (cHSA) with respective pIs of 6.5, 7.3 and 8.0 were made. After eight days of equilibration in a buffer containing labelled native HSA and cHSA, the distribution volumes were calculated relative to that of 51Cr-EDTA, an extracellular tracer. The available volume in fully swollen dermis for native albumin relative to that of the extracellular tracer averaged 0.485+/-0.008 (n=49), with corresponding volumes for cHSA-10 min, cHSA-45 min and cHSA-60 min of 0.554+/-0.012 (n=17), 0.647+/-0.026 (n=17) and 0.718+/-0.021 (n=12), respectively. Increasing the ionic strength of the bathing solution to 1 M NaCl, thereby screening the fixed charges of tissue elements and probes alike, resulted in similar available and thereby excluded volumes of native HSA and neutral cHSA-45 min. These experiments suggest that fixed negative charges, most likely glycosaminoglycans, contribute significantly to interstitial exclusion of charged macromolecules, a phenomenon of importance for hydration of the interstitial fluid phase and therefore for body fluid balance. Moreover, the data indicate that previous findings of similar excluded volumes for the two differently sized major plasma proteins albumin (molecular mass 66 kDa) and IgG (molecular mass 160 kDa) may be explained by a more pronounced electrostatic repulsion of the former by the extracellular matrix.

Mathematical model of renal elimination of fluid and small ions during hyper- and hypovolemic conditions.

This study is concerned with the formulation of a 'kidney module' linked to the plasma compartment of a larger mathematical model previously developed. Combined, these models can be used to predict, amongst other things, fluid and small ion excretion rates by the kidney; information that should prove useful in evaluating values and trends related to whole-body fluid balance for different clinical conditions to establish fluid administration protocols and for educational purposes. The renal module assumes first-order, negative-feedback responses of the kidney to changes in plasma volume and/or plasma sodium content from their normal physiological set points. Direct hormonal influences are not explicitly formulated in this empiric model. The model also considers that the renal excretion rates of small ions other than sodium are proportional to the excretion rate of sodium. As part of the model development two aspects are emphasized (1): the estimation of parameters related to the renal elimination of fluid and small ions, and (2) model validation via comparisons between the model predictions and selected experimental data. For validation, model predictions of the renal dynamics are compared with new experimental data for two cases: plasma overload resulting from external fluid infusion (e.g. infusions of iso-osmolar solutions and/or hypertonic/hyperoncotic saline solutions), and untreated hypo volemic conditions that result from the external loss of blood. The present study demonstrates that the empiric kidney module presented above can provide good short-term predictions with respect to all renal outputs considered here. Physiological implications of the model are also presented.

Endometrial thermal balloon ablation using a high temperature, pulsed system: a mathematical model.

A new endometrial thermal balloon ablation treatment for menorrhagia is modeled mathematically to predict its efficacy and safety. A device preheats a fluid to 173 degrees C within a reservoir external to the uterus, and then pulses this fluid without further heating between the reservoir and the balloon for 2.1 min of treatment time. The model predicted this treatment to result in consistent immediate tissue death (coagulation) depths of 3.4 +/- 0.1 mm for uterine cavities of 7 to 26 mL, and that eventual necrosis (tissue death that would occur 1-5 days post burn) may occur to depths of 6.5 +/- 0.2 mm. Whereas, burn depths varied with uterine cavity volume when a low temperature treatment (constant 75 degrees C for 15 min) was modeled (2.3-2.9 mm and 6.8-8.2 mm, for immediate tissue death and eventual necrosis respectively). Similarly, the high temperature, pulsed treatment was less sensitive to blood perfusion rate than the low temperature treatment. Predicted eventual necrosis depth was 1.5 mm less for the high temperature, pulsed treatment than that predicted for a low temperature treatment (constant 87 degrees C for 7 min) for the same immediate tissue death depth (3.5 mm), indicating that the new high temperature treatment may result in less damage to non targeted tissues.

Development of an agricultural job-exposure matrix for British Columbia, Canada.

Farmers in British Columbia (BC), Canada have been shown to have unexplained elevated proportional mortality rates for several cancers. Because agricultural exposures have never been documented systematically in BC, a quantitative agricultural Job-exposure matrix (JEM) was developed containing exposure assessments from 1950 to 1998. This JEM was developed to document historical exposures and to facilitate future epidemiological studies. Available information regarding BC farming practices was compiled and checklists of potential exposures were produced for each crop. Exposures identified included chemical, biological, and physical agents. Interviews with farmers and agricultural experts were conducted using the checklists as a starting point. This allowed the creation of an initial or 'potential' JEM based on three axes: exposure agent, 'type of work' and time. The 'type of work' axis was determined by combining several variables: region, crop, job title and task. This allowed for a complete description of exposures. Exposure assessments were made quantitatively, where data allowed, or by a dichotomous variable (exposed/unexposed). Quantitative calculations were divided into re-entry and application scenarios. 'Re-entry' exposures were quantified using a standard exposure model with some modification while application exposure estimates were derived using data from the North American Pesticide Handlers Exposure Database (PHED). As expected, exposures differed between crops and job titles both quantitatively and qualitatively. Of the 290 agents included in the exposure axis; 180 were pesticides. Over 3000 estimates of exposure were conducted; 50% of these were quantitative. Each quantitative estimate was at the daily absorbed dose level. Exposure estimates were then rated as high, medium, or low based on comparing them with their respective oral chemical reference dose (RfD) or Acceptable Daily Intake (ADI). This data was mainly obtained from the US Environmental Protection Agency (EPA) Integrated Risk Information System database. Of the quantitative estimates, 74% were rated as low (< 100%) and only 10% were rated as high (>500%). The JEM resulting from this study fills a void concerning exposures for BC farmers and farm workers. While only limited validation of assessments were possible, this JEM can serve as a benchmark for future studies. Preliminary analysis at the BC Cancer Agency (BCCA) using the JEM with prostate cancer records from a large cancer and occupation study/survey has already shown promising results. Development of this JEM provides a useful model for developing historical quantitative exposure estimates where is very little documented information available.