Use of the IEUBK Model for Determination of Exposure Routes in View of Site Remediation

The Integrated Exposure Uptake Biokinetic (IEUBK) model is frequently used to estimate blood lead concentrations of children exposed to lead. Simulations with the IEUBK model were run to estimate the blood lead concentration in children living in the vicinity of a non-ferrous plant, situated in Hoboken, Belgium. Concentrations in soil ranged from 59–2425 mg Pb/kg dm, average concentrations in house dust ranged from 234–73394 mg Pb/kg dm. Measured blood lead concentrations in children aged 2–7 years were between 3 and 35 μ g/dl. Exposure sources were indoor dust in the house and the school, outdoor dust and soil in the home surrounding and at the school's playground, and suspended dust in the air. Soil ingestion values and lead exposure from food were changed to Flemish values. The model was able to predict the measured blood lead concentrations adequately except for the lowest exposure group. Predictions showed a systematic overestimation. Analysis of the data revealed that the neighbourhood's school is an important source of exposure to lead; indoor house dust dominates exposure for children going to school outside the area, because of the high concentrations of lead in indoor dust (3 to 5 times higher than in outdoor soil).     

Soil ingestion rates in children identified by parental observation as likely high soil ingesters

Soil ingestion was estimated over seven consecutive days in a soil tracer‐based mass‐balance methodology in 12 children, aged 1 to 3 years. The children had been identified by parents as likely high soil ingesters based on retrospective observation of daily soil ingestion behavior over the past 30 d. While one of the 12 children displayed high soil ingestion (0.5 to 3.05 g/d) on 4 of 7 d, median soil ingestion rates for the 12 children were comparable to those published in other soil ingestion studies of young children selected for studies based on age and not assumed or observed soil ingestion behavior. The lack of ability of parental judgments to predict high soil ingestion rates represents both an important observation and a significant limitation in current methods to efficiently and accurately identify children who ingest high amounts of soil.     

Screening site contamination usina pathway exposure factors

Radian Corporation conducted an investigation of 29 waste sites at an air force base in New Mexico in partial fulfillment of the RCRA operating permit requirements for the facility. The contract required that the investigation be conducted under the Installation Restoration Program (IRP/CERCLA). In an effort to satisfy both RCRA and CERCLA requirements, a hybrid approach was taken for the risk assessment. Site contaminants ranged from petroleum and unconventional fuels to solvents, pesticides, and PCBs. A screening method was developed to classify the level of contamination at each of the 29 sites based on soil and groundwater sampling results. Under this method, sites were classified as “dirty,”; “clean,”; or “borderline.”; Dirty sites did not require a full‐scale risk assessment because some form of remedial action would be necessary. However, clean sites and borderline sites required a full‐scale risk assessment. For clean sites, the risk assessment served as justification for no further action; for borderline sites, the risk assessment determined whether or not remedial action would be required. The screening method used previously developed multipathway and multimedia models for estimating potential human exposure to environmental contaminants in the air, water, and soil through inhalation, ingestion, and dermal contact routes. Pathway exposure factors (PEFs), which combined information on human physiology, behavior patterns, and models of environmental transport, were used to determine the relationship between the concentration of environmental contaminants and human exposure. The PEF converts concentrations in environmental media to lifetime‐equivalent chronic daily intakes (CDI). Three exposure pathways contributing the greatest proportion of the risk were considered for screening these sites: (1) incidental ingestion of soil; (2) dermal contact with soil; and (3) ingestion of water. This project demonstrated that a screening approach could be used effectively to limit the number of full‐scale risk assessments required for a multisite investigation.     

科尔沁沙地人工杨树林生态服务效能评价

采用定位观测法,系统评价了杨树(Populus simonii)林的防风、抗蚀和滞尘等生态服务效能及其间接价值,同时定量探讨了风速减弱系数与实测林地叶面积指数的关系。结果表明,在研究区主害风(西北风)天气下,林地迎风区6H(H为平均树高)、3H、林地中央、林地背风区林缘、6和8H处2m高度的日平均风速与对照点(流动沙丘)相比均有不同程度减弱,风速减弱系数在18．3％～66．2％之间。林地背风区6H处0．25、0．5、1和2 m 4个高度的月平均风速减弱系数与林地叶面积指数呈显著非线性相关,其间存在良好的三次曲线关系(P<0．0001,R²=0．43～0．94,n=80)。在主害风天气下,林地各观测点的地表日风蚀量与对照点相比大幅度降低,平均降幅85．2％～99．9％。在观测期内,林地中央的日平均降尘量为13.2 kg·hm^-2,而林地迎风区6H处的日平均降尘量为9．9 kg·hm^-2,林地的日滞尘能力约为3．3kg·hm^-2。       

The mutagenic hazards of settled house dust: a review

Given the large proportion of time people spend indoors, the potential health risks posed by chemical contaminants in the indoor environment are of concern. Research suggests that settled house dust (SHD) may be a significant source for indoor exposure to hazardous substances including polycyclic aromatic hydrocarbons (PAHs). Here, we summarize the literature on the mutagenic hazards of SHD and the presence of PAHs in dust. We assess the extent to which PAHs are estimated to contribute to the mutagenicity of SHD, and evaluate the carcinogenic risks associated with exposures to PAHs in SHD. Research demonstrates that SHD has a Salmonella TA98 mutagenic potency of 1000-7000 revertants/g, and contains between 0.5 and 500 microg/g of PAHs. Although they only account for a small proportion of the variability, analyses of pooled datasets suggest that cigarette smoking and an urban location contribute to higher levels of PAHs. Despite their presence, our calculations show that PAHs likely account for less than 25% of the overall mutagenic potency of dust. Nevertheless, carcinogenic PAHs in dust can pose potential health risks, particularly for children who play and crawl on dusty floors, and exhibit hand-to-mouth behaviour. Risk assessment calculations performed in this study reveal that the excess cancer risks from non-dietary ingestion of carcinogenic PAHs in SHD by preschool aged children is generally in the range of what is considered acceptable (1 x 10(-6) to 2 x 10(-6)). Substantially elevated risk estimates in the range 1.5 x 10(-4) to 2.5 x 10(-4) correspond only to situations where the PAH content is at or beyond the 95th percentile, and the risk estimates are adjusted for enhanced susceptibility at early life stages. Analyses of SHD and its contaminants provide an indication of indoor pollution and present important information for human exposure assessments.     

Bioaccessibility and other key parameters in assessing oral exposure to PAH-contaminated soils and dust: A critical review

Soil ingestion is an important pathway for human exposure to polycyclic aromatic hydrocarbon (PAH)-contaminated soils and dust for children (via ingesting hand residue) as well as for adults (via occupational exposure). An appropriate selection of exposure parameter values is essential for having an accurate risk assessment. This review addresses key parameters for estimating oral exposure to PAH-contaminated soils/dust, discusses their variability and uncertainty, and provides recommendations for value selection. Bioaccessibility (contaminant fraction solubilized in gastro-intestinal tract, available for entering bloodstream and reaching target organs) and soil ingestion rate are two key parameters for exposure assessment (usually characterized by large variability and/or uncertainty), followed by exposure frequency/duration and body weight.     

Children’s Phthalate Intakes and Resultant Cumulative Exposures Estimated from Urine Compared with Estimates from Dust Ingestion,Inhalation and Dermal Absorption in Their Homes and Daycare Centers

Total daily intakes of diethyl phthalate (DEP), di(n-butyl) phthalate (DnBP), di(isobutyl) phthalate (DiBP), butyl benzyl phthalate (BBzP) and di(2-ethylhexyl) phthalate (DEHP) were calculated from phthalate metabolite levels measured in the urine of 431 Danish children between 3 and 6 years of age. For each child the intake attributable to exposures in the indoor environment via dust ingestion, inhalation and dermal absorption were estimated from the phthalate levels in the dust collected from the child’s home and daycare center. Based on the urine samples, DEHP had the highest total daily intake (median: 4.42 µg/d/kg-bw) and BBzP the lowest (median: 0.49 µg/d/kg-bw). For DEP, DnBP and DiBP, exposures to air and dust in the indoor environment accounted for approximately 100%, 15% and 50% of the total intake, respectively, with dermal absorption from the gas-phase being the major exposure pathway. More than 90% of the total intake of BBzP and DEHP came from sources other than indoor air and dust. Daily intake of DnBP and DiBP from all exposure pathways, based on levels of metabolites in urine samples, exceeded the Tolerable Daily Intake (TDI) for 22 and 23 children, respectively. Indoor exposures resulted in an average daily DiBP intake that exceeded the TDI for 14 children. Using the concept of relative cumulative Tolerable Daily Intake (TDI_cum), which is applicable for phthalates that have established TDIs based on the same health endpoint, we examined the cumulative total exposure to DnBP, DiBP and DEHP from all pathways; it exceeded the tolerable levels for 30% of the children. From the three indoor pathways alone, several children had a cumulative intake that exceeded TDI_cum. Exposures to phthalates present in the air and dust indoors meaningfully contribute to a child’s total intake of certain phthalates. Such exposures, by themselves, may lead to intakes exceeding current limit values.     

An Arsenic Exposure Model: Probabilistic Validation Using Empirical Data

This paper describes development of a multi-pathway arsenic exposure model. The model uses information on arsenic concentrations in food, water, soil, and dust, combined with estimates of intake and medium-specific absorption. Urinary arsenic is predicted assuming that 60% of absorbed arsenic is excreted in urine under steady state conditions. Fecal arsenic is predicted assuming all unabsorbed arsenic is excreted in feces. We applied this model at a former copper smelter site. Site specific distributions were available for the following parameters: soil and dust arsenic concentration (geometric mean approximately 100 to 200?ppm and 50 to 100?ppm, respectively); the combined childhood soil and dust ingestion rate (geometric mean of 20?mg/d); soil and dust arsenic relative bioavailability (geometric mean 0.20 and 0.28, respectively); exposure duration; water arsenic concentration; air arsenic concentration; and total arsenic in food. Monte Carlo simulation was used to predict daily arsenic uptake and excretion in urine and feces for children. Predicted urine arsenic levels were less than measured levels (73% to 88% of measured values, depending on region of site). On the other hand, predicted fecal arsenic levels exceeded measured levels by a factor of 1.7 to 4.6. We were able to improve the correspondence between predicted and measured arsenic excretion rates by decreasing the assumed value of the combined soil and dust ingestion rate, and increasing the assumed bioavailability of arsenic in soil and dust.     

An audit of behavioral indicators of poor welfare in kenneled dogs in the United Kingdom

This survey-based study describes the prevalence and onset of behavioral indicators of poor welfare in dogs kenneled at United Kingdom rescue shelters. It describes key factors contributing to individual variation in behaviors. At 8 rescue shelters, staff trained in the care of nonhuman animals recorded daily whether dogs in their care displayed each of 15 behaviors. The study originally involved 302 dogs; for the first 14 days, it monitored only 148 dogs daily. The study observed dogs for a maximum of 6 weeks from admittance, observing all 15 behaviors at least once during the first 2 weeks (n = 148). The proportion of dogs observed to perform each behavior differed within the sample. The most commonly observed behavior (24.3% of dogs) was excessive barking. The remaining 14 behaviors ranged from listlessness (20.3%) to repetitive tail-chasing (1.3%). Over the 6 weeks, the proportion observed to pace repetitively and wall bounce increased. The proportion who lacked appetite and displayed fear-associated behavior decreased. Breed differences, gender, and age partially explained variability in the onset and prevalence of behavioral indicators of poor welfare in kenneled dogs.     

An Audit of Behavioral Indicators of Poor Welfare in Kenneled Dogs in the United Kingdom

This survey-based study describes the prevalence and onset of behavioral indicators of poor welfare in dogs kenneled at United Kingdom rescue shelters. It describes key factors contributing to individual variation in behaviors. At 8 rescue shelters, staff trained in the care of nonhuman animals recorded daily whether dogs in their care displayed each of 15 behaviors. The study originally involved 302 dogs; for the first 14 days, it monitored only 148 dogs daily. The study observed dogs for a maximum of 6 weeks from admittance, observing all 15 behaviors at least once during the first 2 weeks (n = 148). The proportion of dogs observed to perform each behavior differed within the sample. The most commonly observed behavior (24.3% of dogs) was excessive barking. The remaining 14 behaviors ranged from listlessness (20.3%) to repetitive tail-chasing (1.3%). Over the 6 weeks, the proportion observed to pace repetitively and wall bounce increased. The proportion who lacked appetite and displayed fear-associated behavior decreased. Breed differences, gender, and age partially explained variability in the onset and prevalence of behavioral indicators of poor welfare in kenneled dogs.     

Plant and soil intake by organic broilers reared in tree- or grass-covered plots as determined by means of n-alkanes and of acid-insoluble ash

Free-range birds such as organic broilers may ingest soil and plants during exploration. The estimation of such intakes is of great interest to quantify possible nutritional supplies and also to evaluate the risk of exposure to parasites or to environmental contaminants. Marker-based techniques are now available and would allow to quantify plant and, especially, soil intake in free-range birds, and this quantification was the aim of this study. Methodologically, the proportion of plants in diet intake was determined first using a method based on n-alkanes. Subsequently, the fraction of soil in the total intake was estimated with a second marker, acid-insoluble ash. This approach was carried out to estimate ingested amounts of plants and soil for five successive flocks of organic broilers, exploring grass-covered yards or those under trees, at two time points for each yard: 51 and 64 days of age. Each factor combination (yard type×period=flock number×age) was repeated on two different yards of 750 broilers each.The birds’ plant intake varied widely, especially on grass-covered yards. The proportion of plant intake was significantly higher on grass-covered plots than under trees and was also affected, but to a lesser extent, by age or flock number. The ingestion of plants would generally not exceed 11 g of DM daily, except two extreme outliers of nearly 30 g. The daily plant intake under trees tended to be lower and never exceeded 7 g of DM. The amount of ingested plants increased significantly for spring flocks. It increased slightly but significantly with age. The proportion of ingested soil was significantly higher under trees than on grass-covered yards. Dry soil intake was generally low with not more than 3 g per day. Only in adverse conditions – that is, older birds exploring yards under trees in winter – soil intake reached the extreme value of nearly 5 g. Broilers on yards under trees ingested significantly more soil than on grass-covered yards with least square means of, respectively, 2.1 and 1.1 g dry soil per day. These quantifications would allow us to evaluate the impact of plant and soil intake in the management of free-range broilers, especially for the management in organic farming systems. Nevertheless, under the two rearing conditions tested in the current study, the quite low proportions of soil intakes would represent a low risk for the safety of the produced food, unless the birds explore yards on heavily contaminated soil.     

Pharmaceutical Contaminants in Potable Water: Potential Concerns for Pregnant Women and Children

There has been increasing concern of late over measurable levels of pharmaceutical contaminants in drinking water. Because most data on water contaminants pertains to aquatic organisms, we wished to assess the risk of these contaminants to human health at currently reported levels. Unlike most other chemicals, there are large amounts of information for the effects of most pharmaceuticals to humans and the current model uses the clinical dose required to cause biological effects as an endpoint to assess risks for pregnant women, children, and the healthy adult population. Twenty-six drugs have been detected in water systems worldwide: 7 in drinking water, 16 in ground water and post-treatment effluent, and 3 in both. Current water treatment practices, clearly, do not always remove pharmaceutical residues. Although healthy adults are unlikely to be adversely affected at the levels of exposure reported, children were shown to have up to eightfold higher risk and may be exposed to several drugs that are contraindicated or not established for safe use in pediatric medicine. The time taken to ingest a single clinically used dose was 3.4–34,000 years. In addition, pregnant women may be exposed to several drugs that are teratogenic (range of % single doses ingested over 36 weeks was 0.0006–12.6%) and in the post-natal period to drugs that are not recommended during breastfeeding. Albeit at low levels, the exposure of pregnant women and children to contraindicated drugs through drinking water is of concern. Further research in this area should focus on integrated ecological and human health consequences of long-term, low-level exposure to pharmaceutical contaminants, particularly in pregnancy and childhood.     

Protection Motivation Theory in Predicting Intention to Engage in Protective Behaviors against Schistosomiasis among Middle School Students in Rural China

Background

Among millions of people who suffer from schistosomiasis in China, adolescents are at increased risk to be infected. However, there is a lack of theory-guided behavioral prevention intervention programs to protect these adolescents. This study attempted to apply the Protection Motivation Theory (PMT) in predicting intentions to engage in protective behaviors against schistosomiasis infection.

Methods

The participants were selected using the stratified cluster sampling method. Survey data were collected using anonymous self-reported questionnaire. The advanced structural equation modeling (SEM) method was utilized to assess the complex relationship among schistosomiasis knowledge, previous risk exposure and protective measures in predicting intentions to engage in protective behavior through the PMT constructs.

Principal Findings

Approximately 70% of participants reported they were always aware of schistosomiasis before exposure to water with endemic schistosomiasis, 6% of the participants reported frequency of weekly or monthly prior exposure to snail-conditioned water. 74% of participants reported having always engaged in protective behaviors in the past three months. Approximately 7% were unlikely or very unlikely to avoid contact with snail-conditioned water, and to use protective behaviors before exposure. Results from SEM analysis indicated that both schistosomiasis knowledge and prior exposure to schistosomiasis were indirectly related to behavior intentions through intrinsic rewards and self-efficacy; prior protective behaviors were indirectly related to behavior intentions through severity, intrinsic rewards and self-efficacy, while awareness had an indirect relationship with behavior intentions through self-efficacy. Among the seven PMT constructs, severity, intrinsic rewards and self-efficacy were significantly associated with behavior intentions.

Conclusions

The PMT can be used to predict the intention to engage in protective behaviors against schistosomiasis. Schistosomiasis intervention programs should focus on the severity, intrinsic rewards and self-efficacy of protection motivation, and also increase the awareness of infection, and enrich the contents of schistosomiasis education.     

Nonsocial behavior of captive infant gorillas

Frequencies of eight nonsocial behaviors (object contact, environmental exploration, mouthing, self-directed behavior, display behavior, solitary behavior, rest, and locomotion) were obtained for 20 infant lowland gorillas (Gorilla gorilla gorilla) between 14 and 36 months of age. They lived in 13 groups in 10 zoological collections. Approximately 12 hours of one-zero data were collected on each animal. Behavioral data were analyzed with regard to the following independent variables: rearing history of the focal animal (mother-reared vs. human-reared), time of day (a.m. vs. p.m.), sex of the focal animal, age of the focal animal, and complexity of the physical and social environment. Results indicated significant differences in the frequency of behaviors within each independent variable, including selfdirected behavior, rest, environmental exploration, and display behavior with rearing history. Additional significant differences in the frequencies of behavior were also found, including mouthing behavior and locomotion with infant age.     

Do Current Standards of Practice in Canada Measure What is Relevant to Human Exposure at Contaminated Sites? II: Oral Bioaccessibility of Contaminants in Soil

Human health risk estimates for sites with contaminated soils are often based on the assumption that the outdoor soil sieved to < 250 μm is a reasonable surrogate for predicting exposures via incidental soil ingestion. In vitro bioaccessibility tests are also increasingly used to “improve” ingestion exposure predictions of contaminants at different sites. However, when considered in terms of factors that influence desorption of contaminants from particles and uptake into humans, available studies indicate that current “standards of practice” with respect to assays of oral bioaccessibility have a number of significant shortcomings, at least in Canada. These shortcomings are discussed and various factors that influence the assessment of bioaccessibility of contaminants in soils are examined. We finish with proposing some minimum data submission requirements to support the application and relevance of bioaccessibility assays at contaminated sites.     

Impact of dust exposure on mixed bacterial cultures and during eukaryotic cell co-culture infections

On a daily basis, humans, and their colonizing microbiome, are exposed to both indoor and outdoor dust, containing both deleterious organic and inorganic contaminants, through dermal contact, inhalation, and ingestion. Recent studies evaluating the dust exposure responses of opportunistic pathogens, such as Escherichia coli and Pseudomonas aeruginosa, revealed significant increases in biofilm formation following dust exposure. In this study, the effects of dust exposure on mixed bacterial cultures as well as HT-29 co-cultures were evaluated. As it was observed in pure, single bacterial cultures earlier, neither indoor nor outdoor dust exposure (at concentrations of 100 μg/mL) influenced the growth of mixed bacterial liquid cultures. However, when in paired mixed cultures, dust exposure increased sensitivity to oxidative stress and significantly enhanced biofilm formation (outdoor dust). More specifically, mixed cultures (E. coli-Klebsiella pneumoniae, K. pneumoniae-P. aeruginosa, and E. coli-P. aeruginosa) exhibited increased sensitivity to 20 and 50 mM of H2O2 in comparison to their pure, single bacterial culture counterparts and significantly enhanced biofilm production for each mixed culture. Finally, bacterial proliferation during a eukaryotic gut cell (HT29) co-culture was significantly more robust for both K. pneumoniae and P. aeruginosa when exposed to both house and road dust; however, E. coli only experienced significantly enhanced proliferation, in HT29 co-culture, when exposed to road dust. Taken together, our findings demonstrate that bacteria respond to dust exposure differently when in the presence of multiple bacterial species or when in the presence of human gut epithelial cells, than when grown in isolation.     

Prozac in the water: Chronic fluoxetine exposure and predation risk interact to shape behaviors in an estuarine crab

Predators exert considerable top‐down pressure on ecosystems by directly consuming prey or indirectly influencing their foraging behaviors and habitat use. Prey is, therefore, forced to balance predation risk with resource reward. A growing list of anthropogenic stressors such as rising temperatures and ocean acidification has been shown to influence prey risk behaviors and subsequently alter important ecosystem processes. Yet, limited attention has been paid to the effects of chronic pharmaceutical exposure on risk behavior or as an ecological stressor, despite widespread detection and persistence of these contaminants in aquatic environments. In the laboratory, we simulated estuarine conditions of the shore crab, Hemigrapsus oregonensis, and investigated whether chronic exposure (60 days) to field‐detected concentrations (0, 3, and 30 ng/L) of the antidepressant fluoxetine affected diurnal and nocturnal risk behaviors in the presence of a predator, Cancer productus. We found that exposure to fluoxetine influenced both diurnal and nocturnal prey risk behaviors by increasing foraging and locomotor activity in the presence of predators, particularly during the day when these crabs normally stay hidden. Crabs exposed to fluoxetine were also more aggressive, with a higher frequency of agonistic interactions and increased mortality due to conflicts with conspecifics. These results suggest that exposure to field‐detected concentrations of fluoxetine may alter the trade‐off between resource acquisition and predation risk among crabs in estuaries. This fills an important data gap, highlighting how intra‐ and interspecific behaviors are altered by exposure to field concentrations of pharmaceuticals; such data more explicitly identify potential ecological impacts of emerging contaminants on aquatic ecosystems and can aid water quality management.     

Soil ingestion in children: Outdoor soil or indoor dust?

Soil ingestion estimates may play a prominent role in exposure estimation for risk assessments involving tightly bound soil contaminants such as dioxin, PCBs, and lead in soil. Since contamination is often localized to specific areas, the relative contribution of ingested soil due to outdoor soil and indoor dust may have a large impact on the risk assessment. This article examines data on 64 preschool children over 2 weeks to estimate the relative contribution of ingested soil from outdoor soil and indoor dust. Four principal methodological approaches are developed and presented to form the estimates, and their relative strengths and weaknesses are discussed.

The four approaches differ in their assumptions and their ability to detail differences in ingestion source. Two approaches (i.e., duration correlation method — approach 1 and group tracer ratio method — approach 2) were used that can only estimate the average ingestion source, where averages are calculated over subjects and weeks. Both of these approaches have sufficient limitations to preclude confidence in the resulting estimates.

The final two approaches (approach 3 — individual tracer ratio method and approach 4 — multiple statistical model method) were able to characterize ingestion source for individual subject‐weeks and offered more plausible estimates of soil ingestion. Greater emphasis is placed on approach 3 since it was biologically plausible and conceptually straightforward. Approach 3 indicated that 49.2% ± 29.2% of the residual fecal tracers were estimated to be of soil origin. These findings, which represent the first quantitative differentiation of soil vs. dust ingestion, have considerable application for a variety of environmental settings requiring exposure assessment.     

Revisiting Dust and Soil Ingestion Rates Based on Hand-to-Mouth Transfer

Soil ingestion rates calculated using a tracer-based mass balance approach may carry considerable study errors, insensitivities, and “artefacts” of analysis that result in significant uncertainty. These same soil ingestion rates are often used as surrogates for dust ingestion rates. Therefore, a more direct and mechanistic method was developed to estimate soil and dust ingestion rates. The soil and dust ingestion rates were calculated using measures of: particle loading to indoor surfaces; fraction transferred to the hands; hand surface area; fraction of hand surface area that may be mouthed or contact food; frequency of hand-to-mouth events, amount dissolved by saliva; and exposure time. Adapted specifically for the Canadian context, estimated mean indoor dust ingestion rates range from 2.2 mg/d for teenagers to 41 mg/d for toddlers; mean soil ingestion rates range from 1.2 mg/d for seniors to 23 mg/d for children. Combined soil and dust ingestion rates ranged from 3.8 mg/d for seniors to 61 mg/d for toddlers. These ingestion rates are lower than values adopted by most agencies. These ingestion rates are mechanistic, can be adjusted on a site-specific basis, can be modified into an hourly rate and are presented as a more realistic alternative to traditional mass balance approaches.

[Supplementary materials are available for this article. Go to the publisher's online edition of Human and Ecological Risk Assessment to view the free supplementary files.]     

Circadian Time-Dependent Response of Childhood Lymphoblastic Leukemia to Chemotherapy: A Long-Term Follow-up Study of Survival

The evolution of 118 children treated for acute lymphoblastic leukemia between 1976 and 1984, and followed until 1991, was reviewed. Maintenance chemotherapy consisted of daily 6-mercaptopurine (6-MP), weekly methotrexate (MTX), and monthly vincristine and prednisone. Eighty-two children took 6-MP and MTX in the morning, and 36 took them in the evening. Disease-free survival, as determined by Kaplan-Meier analysis, was better for children on evening chemotherapy. Regression analysis (Cox proportional hazards model, with evening versus morning schedule as exposure variable, and age at diagnosis, leucocytosis at diagnosis, and sex as covariates) showed that for those surviving free of disease for longer than 78 weeks, the risk of relapse was 2.56 times greater for the morning schedule than for the evening one.