Predicted indoor radon concentrations from a Monte Carlo simulation of 1,000,000 granite countertop purchases

Previous research examining radon exposure from granite countertops relied on using a limited number of exposure scenarios. We expanded upon this analysis and determined the probability that installing a granite countertop in a residential home would lead to a meaningful radon exposure by performing a Monte Carlo simulation to obtain a distribution of potential indoor radon concentrations attributable to granite. The Monte Carlo analysis included estimates of the probability that a particular type of granite would be purchased, the radon flux associated with that type, the size of the countertop purchased, the volume of the home where it would be installed and the air exchange rate of that home. One million countertop purchases were simulated and 99.99% of the resulting radon concentrations were lower than the average outdoor radon concentrations in the US (14.8 Bq m(-3); 0.4  pCi l(-1)). The median predicted indoor concentration from granite countertops was 0.06 Bq m(-3) (1.59 × 10(-3) pCi l(-1)), which is over 2000 times lower than the US Environmental Protection Agency's action level for indoor radon (148 Bq m(-3); 4 pCi l(-1)). The results show that there is a low probability of a granite countertop causing elevated levels of radon in a home.

A longitudinal investigation of aggregate oral intake of copper

Four-day composite solid food and beverage duplicate plates and 1-L samples of drinking water were collected from a stratified random sample of 80 individuals as part of the National Human Exposure Assessment Survey in Maryland. The media were obtained from each participant in up to six equally spaced sampling cycles over a year and analyzed for copper by inductively coupled plasma mass spectrometry. Copper concentrations (microg/kg) and consumption rates (kg/d) of solid food, beverage and drinking water were used to derive average daily aggregate oral intake of copper (microg/d). The mean aggregate copper intake of 263 measurements obtained from 68 people was 923.2 +/- 685.6 microg/d (mean +/- SD). Intake through solid food accounted for the majority of aggregate daily intake of copper contributing 87% on average. According to results from mixed model analysis of variance procedures, the mean log-transformed average daily copper intake in each medium except beverage exhibited significant (P < 0.05) variability among sampling cycles. Between-person variability accounted for 50% of the total variance in aggregate copper intake. As measured by the coefficient of variation, distributions of copper intake consisting of one observation per individual were more variable than the distribution consisting of the long-term average intake for each person. These results suggest that estimates of the fraction of a population at risk from chronic copper deficiency or excess copper intake can be overestimated if based upon short-term measures of copper intake. In addition, these results indicate that longitudinal information is required for accurate assessment of aggregate oral intake of copper for an individual.

Performance of electronic flow rate meters used for calibration of air sampling pumps

Electronic flow rate meters (EFRMs) have been used by industrial hygienists for more than 20 years and are useful because they reduce the time required to calibrate air sampling pumps. This study compared the variability of the traditional bubble burette meter with electronic flow meters and simultaneously compared several EFRMs under different calibration conditions. The flow rates of air sampling pumps were set using a standard bubble burette meter at flow rates of 2 or 50 mL/min using two pressure drops, 2 inches water and 10 inches water. Four airflow rate meters (Bios DryCal, A.P. Buck mini-Buck, MSA Accuflow, and Sensidyne Gilibrator) were concurrently compared at each of the pump flow rate and pressure drop combinations. Results indicated that the standard bubble burette method is more variable than the EFRMs and that the flow rates given by the EFRMs were significantly different (p<0.0001) at both the high and low flow rates. Although the calibrators gave significantly different flow rates, the difference was within the acceptable air sampling pump error of +/- 5%.

Dietary exposure to chlorpyrifos and levels of 3,5,6-trichloro-2-pyridinol in urine

Information on associations between chlorpyrifos residues in food and personal exposure to chlorpyrifos would be valuable for evaluating the relationship between personal exposure and possible health effects. We used food consumption records, chlorpyrifos levels in duplicate plates, and measures of 3,5,6-trichloro-2-pyridinol (TCPy) in urine obtained from human volunteers in the National Human Exposure Assessment Survey in Maryland (NHEXAS-MD) to evaluate a food consumption-chemical residue model for estimating dietary intake of chlorpyrifos. Model inputs were the NHEXAS-MD food consumption records and chlorpyrifos residues in specific foods measured in the U.S. Food and Drug Administration Total Diet Study (TDS) market baskets from 1993 to 1997. The estimated mean and standard deviation of chlorpyrifos concentration (microg/kg) in duplicate plates (n=203) were within 20% and 50%, respectively, of the corresponding parameters of measured chlorpyrifos levels. However, predicted and measured concentrations in the 78 duplicate plates with detectable levels of chlorpyrifos were not significantly associated according to Spearman correlation analysis (r=0.04, p=0.7667) and linear regression (p=0.2726). Measured and estimated chlorpyrifos intakes for observations with non-zero values for each intake measure (n=71) were moderately associated on a rank (Spearman's r=0.24, p=0.0462) and linear basis (regression r(2)=0.07, p=0.0242). Measured intakes of chlorpyrifos from food and urinary TCPy were significantly correlated in rank order (n=87, Spearman's r=0.30, p=0.0041) and linear (n=87, Pearson's r=0.22, p=0.0409) analyses. Correlation coefficients between estimated intake of chlorpyrifos from food and TCPy were significantly different from zero (n=87; Spearman's r=0.22, p=0.0393; Pearson's r=0.21, p=0.0479). Comparing mean measured chlorpyrifos intake from food (0.46 microg/day) to mean estimated TCPy excretion via urine (6.3 microg/day), dietary intake of chlorpyrifos accounted for approximately 7% of TCPy in this population. These findings suggest the food consumption-chemical residue model can yield reasonably accurate estimates of the population distribution of dietary chlorpyrifos intake, but has little ability to predict dietary exposure for individuals; and that intake of chlorpyrifos from food is a minor contributor to TCPy in urine.

A comparison of four gravimetric fine particle sampling methods

A study was conducted to compare four gravimetric methods of measuring fine particle (PM2.5) concentrations in air: the BGI, Inc. PQ200 Federal Reference Method PM2.5 (FRM) sampler; the Harvard-Marple Impactor (HI); the BGI, Inc. GK2.05 KTL Respirable/Thoracic Cyclone (KTL); and the AirMetrics MiniVol (MiniVol). Pairs of FRM, HI, and KTL samplers and one MiniVol sampler were collocated and 24-hr integrated PM2.5 samples were collected on 21 days from January 6 through April 9, 2000. The mean and standard deviation of PM2.5 levels from the FRM samplers were 13.6 and 6.8 microg/m3, respectively. Significant systematic bias was found between mean concentrations from the FRM and the MiniVol (1.14 microg/m3, p = 0.0007), the HI and the MiniVol (0.85 microg/m3, p = 0.0048), and the KTL and the MiniVol (1.23 microg/m3, p = 0.0078) according to paired t test analyses. Linear regression on all pairwise combinations of the sampler types was used to evaluate measurements made by the samplers. None of the regression intercepts was significantly different from 0, and only two of the regression slopes were significantly different from 1, that for the FRM and the MiniVol [beta1 = 0.91, 95% CI (0.83-0.99)] and that for the KTL and the MiniVol [beta1 = 0.88, 95% CI (0.78-0.98)]. Regression R2 terms were 0.96 or greater between all pairs of samplers, and regression root mean square error terms (RMSE) were 1.65 microg/m3 or less. These results suggest that the MiniVol will underestimate measurements made by the FRM, the HI, and the KTL by an amount proportional to PM2.5 concentration. Nonetheless, these results indicate that all of the sampler types are comparable if approximately 10% variation on the mean levels and on individual measurement levels is considered acceptable and the actual concentration is within the range of this study (5-35 microg/m3).

Ambient air quality at the site of a former manufactured gas plant

Prior to the 1950's, manufactured gas was commercially produced from the pyrolysis of coal, coke, and oil at facilities that are termed manufactured gas plants (MGPs). The constituents of residual coal tar present on many MGP sites are an environmental health concern because of their toxicity and the possibility for their off-site migration via water and air. Atmospheric concentrations of five volatile organic compounds (VOCs, e.g., benzene), sixteen polycyclic aromatic hydrocarbons (PAHs, e.g., naphthalene) and particulate matter less than 10 microns in aerodynamic diameter (PM10) were measured at the site of a former MGP. Air samples were obtained before, during, and after excavation of subterranean coal tar at the site. The results of this investigation indicate that subterranean coal tar was not a primary source of VOCs and PAHs in the local atmosphere before or after remediation of the site. However, excavation, treatment, blending, and transfer of the coal tar during remediation generated concentrations of selected aromatic and semi-volatile organic compounds that were substantially greater than typical ambient levels. In addition, these data suggest that blending and mixing of coal tars could lead to exceedance of the U.S. National Ambient Air Quality Standard for PM10, although additional research is required to fully evaluate this possibility. Nuisance odors associated with the site remediation were likely the result of naphthalene and possibly isomers of xylene. Air pollutant concentrations measured adjacent to the excavation area and at the site perimeter during remediation activities were less than the relevant occupational and environmental exposure limits.

Longitudinal investigation of dietary exposure to selected pesticides

Between September 1995 and September 1996, 4-day composite duplicate plate samples (379 solid food samples and 303 beverage samples) were obtained from a stratified random sample of 75 individuals in Maryland and analyzed for the presence of 10 pesticides. Samples were collected in each of six approximately equally spaced cycles as part of a larger pilot investigation of longitudinal exposure to pesticides and other elements. Chlorpyrifos was detected in 38.3% of the solid food samples, malathion in 75.2%, and p,p'-DDE in 21.4%. Other pesticides were detected in less than 10% of the solid food samples. Pesticide residues were not detected in duplicate beverage samples. In solid food samples, the mean concentration of chlorpyrifos was 0.7 (SD 1.7) microg/kg, 1.8 (2.1) for malathion, and 0.2 (0.6) for p,p'-DDE. The detection rate and mean concentration of chlorpyrifos, malathion, and p,p'-DDE varied by a factor of 2-3 among sampling cycles and significantly according to results from several statistical analyses. Co-occurrence of chlorpyrifos and malathion in solid food samples was found relatively frequently and also varied with time. Pesticides were detected in food samples with greatest frequency in spring and summer months and with lowest frequency in winter months. These results support the hypothesis that 4-day average exposure to chlorpyrifos and malathion varies over time for this population mean and for individual members of the population and that correlation between exposures to these two organophosphate pesticides can occur. The measurements of pesticide levels in duplicate plate samples presented here can be used to evaluate and set parameters for dietary exposure models.

Analysis of dietary intake of selected metals in the NHEXAS-Maryland investigation

As part of a large pilot investigation of multimedia exposure to several classes of environmental contaminants, the National Human Exposure Assessment Survey (NHEXAS)-Maryland study, we collected 388 semiquantitative food checklists and duplicate diet solid food samples, analyzed for arsenic, cadmium, chromium, and lead concentrations, from 80 individuals in Maryland in 1995-1996 in a repeated measures design. Here we explore several methods to infer foods most strongly associated with concentrations of these metals observed in the duplicate diet in our data set. We employed two techniques in which logarithmically transformed metal concentrations in the duplicate diet were regressed on individual food item consumption using algorithms designed to identify the foods most associated with the observed duplicate diet concentrations. We also employed an alternative strategy in which foods to be used as independent variables in regression were selected using data collected in national food consumption and residue surveys, with regression procedures proceeding with the selected foods in a similar manner. The concordance of foods selected as major predictors among these three techniques is noteworthy and is discussed. Finally, the Dietary Exposure Potential Model (DEPM) was used with the Dietary Checklist data to predict duplicate diet concentrations within our sample. A comparison between the predicted values and those observed gave R(2) values of 0.180, 0.206, and 0.076 for As, Cd, and Pb, respectively (p < 0.0001 in all cases). We discuss the significance of these observations and the implications for dietary-exposure-based risk analysis and dietary intake epidemiology.

Longitudinal investigation of exposure to arsenic, cadmium, and lead in drinking water

Arsenic, cadmium, and lead have been associated with various forms of cancer, nephrotoxicity, central nervous system effects, and cardiovascular disease in humans. Drinking water is a well-recognized pathway of exposure to these metals. To improve understanding of the temporal dimension of exposure to As, Cd, and Pb in drinking water, we obtained 381 samples of tap and/or tap/filtered water and self-reported rates of drinking water consumption from 73 members of a stratified random sample in Maryland. Data were collected at approximately 2-month intervals from September 1995 through September 1996. Concentrations of As (range < 0.2-13.8 microg/L) and Pb (< 0.1-13.4 microg/L) were within the ranges reported for the United States, as were the rates of drinking water consumption (median < 0.1-4.1 L/day). Cd was present at a detectable level in only 8.1% of the water samples. Mean log-transformed concentrations and exposures for As and Pb varied significantly among sampling cycles and among respondents, as did rates of drinking water consumption, according to a generalized linear model that accounted for potential correlation among repeated measures from the same respondent. We used the intraclass correlation coefficient of reliability to attribute the total variance observed for each exposure metric to between-person and within-person variability. Between-person variability was estimated to account for 67, 81, and 55% of the total variance in drinking water consumption, As exposure (micrograms per day), and Pb exposure (micrograms per day), respectively. We discuss these results with respect to their implications for future exposure assessment research, quantitative risk assessment, and environmental epidemiology.

Air quality and pediatric emergency room visits for asthma in Atlanta, Georgia, USA

Pediatric emergency room visits for asthma were studied in relation to air quality indices in a spatio-temporal investigation of approximately 130,000 visits (approximately 6,000 for asthma) to the major emergency care centers in Atlanta, Georgia, during the summers of 1993-1995. Generalized estimating equations, logistic regression, and Bayesian models were fitted to the data. In logistic regression models comparing estimated exposures of asthma cases with those of the nonasthma patients, controlling for temporal and demographic covariates and using residential zip code to link patients to spatially resolved ozone levels, the estimated relative risk per 20 parts per billion (ppb) increase in the maximum 8-hour ozone level was 1.04 (p < 0.05). The estimated relative risk for particulate matter less than or equal to 10 microm in aerodynamic diameter (PM10) was 1.04 per 15 microg/m3 (p < 0.05). Exposure-response trends (p < 0.01) were observed for ozone (>100 ppb vs. <50 ppb: odds ratio = 1.23, p = 0.003) and PM10 (>60 microg/m3 vs. <20 microg/m3: odds ratio = 1.26, p = 0.004). In models with ozone and PM10, both terms became nonsignificant because of collinearity of the variables (r= 0.75). The other analytical approaches yielded consistent findings. This study supports accumulating evidence regarding the relation of air pollution to childhood asthma exacerbation.

Longitudinal investigation of exposure to arsenic, cadmium, chromium and lead via beverage consumption

Semi-quantitative food checklists and duplicate beverage samples were collected from up to 80 individuals in Maryland in 1995-1996 in as many as six approximately equally spaced sampling cycles as part of a pilot longitudinal exposure investigation. The duplicate beverage samples were homogenized and analyzed for arsenic (As), cadmium (Cd), chromium (Cr) and lead (Pb) using inductively coupled plasma mass spectrometry (ICP-MS). Metal concentrations (microg/kg) and weights of the duplicate beverage samples (kg/day) were used to derive average daily exposure (microg/day) for each metal. Mixed models and generalized linear models were used to evaluate temporal and population variability of the beverage consumption rates, the log-transformed metal concentrations in the beverage samples, and the associated exposures. The mean number of beverage servings consumed per day was 3.4 (SD 1.9). The temporal variability of the total beverage consumption rates was found to be significant (p = 0.0476). As, Cd, Cr, and Pb were present at quantifiable levels in 93.5, 76.0, 93.5, and 96.7% of the beverage samples, respectively. The mean concentration in the samples was 2.0 (SD 4.4) microg/kg for As, 0.9 (1.6) for Cd, 29.2 (138.5) for Cr, and 2.0 (2.4) for Pb. The mean log-transformed concentrations for As, Cr and Pb and exposure for As varied by as much as a factor of 3 across sampling cycles and were statistically significantly different (p<0.05). Concentrations and exposures of all four metals varied significantly among participants. These findings are discussed with respect to the data collection methods, results from comparable studies, and implications for exposure and risk assessment.

Temporal variability of microenvironmental time budgets in Maryland

Information on human time-activity patterns is often required to interpret environmental exposure data fully and to implement exposure assessment models. Data on short-term time-activity patterns for individuals, such as 1-day measurements, are relatively abundant. The reliability of such data for use in chronic exposure (e.g., 1 or more years) assessments performed for evaluation of health risks is not well understood. As part of the NHEXAS-Maryland investigation, daily time budget data for seven microenvironments were collected from 80 people during as many as six 1-week Cycles over a 12-month period. The data were summarized and analyzed statistically by sampling Cycle, day of week, and individual to characterize long-term average microenvironmental time budgets and to identify their determinants. Median times spent in transit, indoors at home, outside at home, indoors at work or school, outdoors at work or school, indoors at other locations, and outdoors at other locations were found to vary significantly, although not substantively in many cases, by time of year (i.e., Cycle), by day of week, and by individuals. Time budgets for most of the microenvironments also exhibited significant variability by gender, age group, education level, annual household income, and work status. The results indicate that short-term (e.g., 1-day) measures of microenvironmental time budgets for individuals are unlikely to be representative of their long-term patterns. Thus, health risk or epidemiological assessments performed for a population mean or specific quantile may be relatively insensitive to when time budget data were collected. However, the accuracy of such assessments performed for individuals is likely to be greatly improved by collection of time budget data from numerous points in time.

A longitudinal investigation of selected pesticide metabolites in urine

As part of a longitudinal investigation of environmental exposures to selected chemical contaminants, concentrations of the pesticide metabolites 1-naphthol (INAP), 3,5,6-trichloro-2-pyridinol (TCPY), malathion dicarboxylic acid (MDA), and atrazine mercapturate (AM) were measured in repeated samples obtained from 80 individuals in Maryland during 1995-1996. Up to six urine samples were collected from each individual at intervals of approximately 8 weeks over a 1-year period (i.e., one sample per participant in each of six cycles). INAP (median=4.2 microg/l and 3.3 microg/g creatinine) and TCPY (median=5.3 microg/l and 4.6. microg/g creatinine) were present in over 80% of the samples, while MDA and AM were detected infrequently (6.6% and <1% of samples, respectively). Geometric mean (GM) concentrations of INAP in urine did not vary significantly among sampling cycles. In contrast, GM concentrations of TCPY were significantly greater in samples collected during the spring and summer of 1996 than in the preceding fall and winter. Repeated measurements of INAP and TCPY from the same individual over time were highly variable. The average range of INAP and TCPY concentrations from the same individual were approximately 200% and 50% greater than the respective population mean levels. Geometric mean (GM) TCPY concentrations differed significantly between Caucasian (n=42, GM=5.7 microg/g creatinine) and African-American (n=11, GM=4.0 microg/g) participants and among education levels, but were not significantly different among groups classified by gender, age, or household income. In future research, environmental measurements of the parent compounds and questionnaire data collected concurrently with the biomarker data will be used to characterize the determinants of variability in the urinary pesticide metabolite levels.

A longitudinal investigation of solid-food based dietary exposure to selected elements

As part of a longitudinal investigation of environmental exposures to selected chemical contaminants, the National Human Exposure Assessment Survey (NHEXAS), food consumption and duplicate diet samples were obtained in each of six sampling cycles from up to 80 individuals in Maryland during 1995-1996. Duplicate diet samples were weighed and analyzed for arsenic, cadmium, chromium and lead and were used to derive average daily intakes of each element. Mean log-transformed concentrations of arsenic and cadmium in duplicate diet samples and derived intakes of chromium were found to vary significantly among sampling cycles. Repeated observations of dietary exposure metrics from the same individual over time were highly variable. The results suggest that distributions of dietary exposure to arsenic and cadmium do vary for a population within a 1-year period, while those for chromium and lead do not. This may result in single measurements of exposure being sufficient to characterize population variability for these latter two elements. However, even for those elements not displaying statistically significant temporal variability for the population, a single dietary exposure measurement may still not be sufficient to characterize accurately chronic dietary exposure levels for individuals.

Employee exposure to diesel exhaust in the electric utility industry

The purpose of this study was to assess diesel exhaust exposures in the electric utility industry and to compare these findings with worker exposures reported in other industries and to proposed and established occupational exposure limits. Two sampling approaches were used: particulates were analyzed for elemental (EC) and organic (OC) carbon via the thermal-optical method; and gaseous components (NO2, SO2, NO, and CO) were determined using a direct reading instrument, the Metrosonics pm-7400. Concentrations of the gases were all well within established occupational exposure levels. The EC percentage of the total carbon was generally lower than results reported from other studies resulting in OC levels representing a higher percentage of the total carbon concentrations. Smokers had higher average OC exposure (79 micrograms/m3) than nonsmokers (57 micrograms/m3), but cigarette smoke did not contribute to EC levels in this study (smokers and nonsmokers = 3 micrograms/m3). Two of 120 individual personal exposure levels were found to exceed the proposed threshold limit value of 150 micrograms/m3 for total particulate, but geometric mean levels were found to be significantly less than the proposed value. Questions are raised concerning the use of EC as the sole surrogate for estimating diesel content for comparison with an exposure standard.

Evaluation of a food frequency questionnaire-food composition approach for estimating dietary intake of inorganic arsenic and methylmercury

Inorganic arsenic intake in 969 men and women and methylmercury intake in 785 men and women from across the United States were assessed by a semiquantitative food frequency questionnaire, in combination with a database for the content of those elements in foods, and by toenail concentrations of arsenic and mercury. In addition, empirical weights for foods on the dietary questionnaire were derived from multivariate regression models to estimate associations between diet and toenail arsenic and mercury levels, independent of the assumptions about inorganic arsenic and methylmercury in foods, which are based upon limited residue measurements. The use of empirical weights significantly improved the correlation of arsenic consumption with toenail arsenic levels (r = 0.33, P = 0.0001), compared with the weak correlation obtained using the food residue method to calculate intake (r = 0.15, P = 0.0001). Mercury consumption computed using empirical weights yielded a significant correlation with toenail arsenic (r = 0.42, P = 0.001), similar to the correlation using energy-adjusted intake calculated from food residue tables (r = 0.35, P = 0.001). These results illustrate the potential use of empirically derived weights for foods in estimating toenail levels of selected heavy metals and support the validity of published food residue data that are used to estimate mercury consumption.

Dietary exposures to selected metals and pesticides

Average daily dietary exposures to 11 contaminants were estimated for approximately 120,000 U.S. adults by combining data on annual diet, as measured by a food frequency questionnaire, with contaminant residue data for table-ready foods that were collected as part of the annual U.S. Food and Drug Administration Total Diet Study. The contaminants included in the analysis were four heavy metals (arsenic, cadmium, lead, mercury), three organophosphate pesticides (chlorpyrifos, diazinon, malathion), and four organochlorine pesticides (dieldrin, p,p'-DDE, lindane, heptachlor epoxide). Dietary exposures to these contaminants were highly variable among individuals, spanning two to three orders of magnitude. Intraindividual exposures to the metals, organophosphates, and organochlorines were estimated to be strongly correlated; Pearson's correlation coefficients ranged from 0.28 for lindane:dieldrin to 0.84 for lead:mercury. For some of the compounds (e.g., arsenic and dieldrin), a substantial fraction of the population was estimated to have dietary intakes in excess of health-based standards established by the EPA. Before use for risk assessment or epidemiologic purposes, however, the validity of the exposure estimates must be evaluated by comparison with biological indicators of chronic exposure. Because of their low detection rate in table-ready foods, the estimated distributions of exposures for dieldrin, p,p'-DDE, heptachlor epoxide, lindane, diazinon, and chlorpyrifos were found to be sensitive to assumed values for nondetect samples. Reliable estimates of the population distribution of dietary exposures to most other contaminants cannot be made currently, due to their low rate of detection in table-ready foods. Monitoring programs that use more sensitive study designs and population-based assessments for other subpopulations should be a priority for future research.

Dietary exposures to selected metals and pesticides

Average daily dietary exposures to 11 contaminants were estimated for approximately 120,000 U.S. adults by combining data on annual diet, as measured by a food frequency questionnaire, with contaminant residue data for table-ready foods that were collected as part of the annual U.S. Food and Drug Administration Total Diet Study. The contaminants included in the analysis were four heavy metals (arsenic, cadmium, lead, mercury), three organophosphate pesticides (chlorpyrifos, diazinon, malathion), and four organochlorine pesticides (dieldrin, p,p'-DDE, lindane, heptachlor epoxide). Dietary exposures to these contaminants were highly variable among individuals, spanning two to three orders of magnitude. Intraindividual exposures to the metals, organophosphates, and organochlorines were estimated to be strongly correlated; Pearson's correlation coefficients ranged from 0.28 for lindane:dieldrin to 0.84 for lead:mercury. For some of the compounds (e.g., arsenic and dieldrin), a substantial fraction of the population was estimated to have dietary intakes in excess of health-based standards established by the EPA. Before use for risk assessment or epidemiologic purposes, however, the validity of the exposure estimates must be evaluated by comparison with biological indicators of chronic exposure. Because of their low detection rate in table-ready foods, the estimated distributions of exposures for dieldrin, p,p'-DDE, heptachlor epoxide, lindane, diazinon, and chlorpyrifos were found to be sensitive to assumed values for nondetect samples. Reliable estimates of the population distribution of dietary exposures to most other contaminants cannot be made currently, due to their low rate of detection in table-ready foods. Monitoring programs that use more sensitive study designs and population-based assessments for other subpopulations should be a priority for future research.

A population-based exposure model for benzene

A model of daily-average inhalation exposures and total-absorbed doses of benzene to members of large populations was developed as part of a series of multimedia exposure and absorbed dose models. The benzene exposure and dose model is based upon probabilistic rather than sequential simulation of time-activity patterns, a simpler approach to modeling personal benzene exposures than other existing models. An important innovation of the benzene model is the incorporation of an anthropometric module for generating correlated exposure factors used to estimate absorbed doses occurring from inhalation, ingestion, and dermal absorption of benzene. A preliminary validation exercise indicates that the benzene model produces reasonable estimates of the distribution of benzene personal air concentrations expected for a large population. Uncertainty about specific percentiles of the predicted distributions of personal air concentrations was found to be dominated by uncertainty about microenvironmental benzene concentrations rather than time-activity patterns, and uncertainty about total absorbed doses was dominated by a lack of knowledge about the true absorption coefficient for benzene in the lung rather than knowledge gaps about microenvironmental concentrations or intake rates. The results of this modeling effort have implications for environmental control decisions, including evaluation of source control options, characterization of population and individual risk, and allocation of resources for future studies.

Chronic anterior cruciate ligament deficiency. Long-term results of MacIntosh's lateral substitution reconstruction

The lateral substitution reconstruction operation described by MacIntosh has been evaluated in 27 patients with chronic anterior cruciate ligament deficiency of the knee. The results, at an average of 11.3 years after operation, have been assessed by a scoring system which allocates a maximum of 25 points each for function and for clinical evaluation. Emphasis was placed on subjective giving way and objective evidence of a positive anterior drawer sign and a positive lateral pivot shift test. A score of 46 to 50 was classified as excellent, 41 to 46 as fair, and less than 41 was a poor result: 52% scored excellent, 26% fair and 22% were poor. Most of those with poor results had had evidence of osteoarthritis at the time of operation. Despite the recorded scores, no less than 75% of the patients at long-term follow-up were subjectively improved, and able to maintain an active life style.

Distal femoral varus osteotomy for valgus deformity of the knee

Twenty-four patients who had degenerative arthritis of the lateral compartment of the knee that was associated with a valgus deformity and a superolateral tilt of the joint line were treated by distal femoral varus osteotomy. A surgical technique that was designed to produce a horizontal joint line and a tibiofemoral angle of zero degrees is described. At an average length of follow-up of four years, twenty-two of twenty-four patients had a successful result as judged by our protocol for evaluation. One osteotomy had to be revised for failure of fixation, and one patient had a pulmonary embolism that had a satisfactory outcome after the administration of anticoagulants. One patient required manipulation of the knee at six months. The simple surgical technique that we used was effective in realigning the femoral with the tibial axis in patients who had a valgus deformity of the knee, a superolateral tilt of the joint line, and osteoarthritis of the lateral compartment.

The lateral pivot shift: a symptom and sign of anterior cruciate ligament insufficiency

The lateral pivot shift(LPS) is a special form of lateral compartment instability arising from anterior cruciate insufficiency. It is characterized by anterior subluxation of the tibial plateau out from beneath the lateral femoral condyle. As a consequence of this form of instability, deleterious changes of the knee joint take place, including meniscal tears, and articular cartilage erosions. The eventual result of continued symptomatic instability is late osteoarthritis of the knee. LPS is the most prominent form of instability of the knee in patients complaining of "giving way" of the knee, and recovery from severe soft-tissue injury to the knee joint.

Joint débridement--a complement to high tibial osteotomy in the treatment of degenerative arthritis of the knee

The management of unicompartmental osteoarthritis of the knee by high tibial osteotomy is enhanced by an associated joint débridement. A review of 120 patients who underwent the combined procedure, with follow-up to thirteen years, indicated that good or satisfactory results may be achieved in 82 per cent and that such results may be maintained over a prolonged period of review. This paper summarizes a long-term review of a series of one of us (D. L. M.), who since 1961 has practiced the combined procedure of tibial osteotomy and open joint débridement. The patient group was reviewed by him one year following surgery and then independently by the second author (R. P. W) in 1974, when 105 of the original 120 patients were available for detailed follow-up. Controversy surrounds the role of débridement when associated with osteotomy. This paper discusses both the rationale for and the results of combining these procedures. The over-all results confirm that these procedures are indeed complementary.

Postoperative flexion contracture of the knee: a simple technique for its treatment

Flexion contracture is not a common problem following knee surgery, but it can be severe enough to jeopardize the success of the operation. With the Beath technique a stove-pipe cast is windowed anteriorly and the cast is padded behind the leg, which is then gently wedged into extension. In this way many flexion contractures can be gently and easily overcome. In addition, the need for serial casting or forcible manipulation is obviated and the overall rehabilitation program is unimpeded. In this paper the authors report two illustrative cases, and discuss the advantages and applications of the Beath technique.

THE USE OF THE HEMIARTHROPLASTY PROSTHESIS FOR ADVANCED OSTEOARTHRITIS AND RHEUMATOID ARTHRITIS OF THE KNEE

1. Hemiarthroplasty is a method of dealing with painful deformities of advanced osteoarthritis and rheumatoid arthritis of the knee.

2. The indications and contra-indications for this procedure are discussed. Careful selection of patients is essential.

3. The technique of operation and management after operation are described.

4. The results of such a procedure, as done by one surgeon, are given. Good results have been obtained in 80 per cent of the osteoarthritic knees and in 69 per cent of the rheumatoid knees.

5. The complications, place of associated operations and value of revision procedures are discussed.