Polybrominated diphenyl ether (PBDE) concentrations and resulting exposure in homes in California: relationships among passive air,surface wipe and dust concentrations,and temporal variability

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in furniture foam, electronics, and other home furnishings. A field study was conducted that enrolled 139 households from California, which has had more stringent flame retardant requirements than other countries and areas. The study collected passive air, floor and indoor window surface wipes, and dust samples (investigator collected using an HVS3 and vacuum cleaner) in each home. PentaBDE and BDE209 were detected in the majority of the dust samples and many floor wipe samples, but the detection in air and window wipe samples was relatively low. Concentrations of each PBDE congener in different indoor environmental media were moderately correlated, with correlation coefficients ranging between 0.42 and 0.68. Correlation coefficients with blood levels were up to 0.65 and varied between environmental media and age group. Both investigator‐collected dust and floor wipes were correlated with serum levels for a wide range of congeners. These two sample types also had a relatively high fraction of samples with adequate mass for reliable quantification. In 42 homes, PBDE levels measured in the same environmental media in the same home 1 year apart were statistically correlated (correlation coefficients: 0.57–0.90), with the exception of BDE209 which was not well correlated longitudinally.     

Contaminant exposure and effects in pinnipeds: implications for Steller sea lion declines in Alaska

After nearly 3 decades of decline, the western stock of Steller sea lions (SSL; Eumetopias jubatus) was listed as an endangered species in 1997. While the cause of the decline in the 1970s and 1980s has been attributed to nutritional stress, recent declines are unexplained and may result from other factors including the presence of environmental contaminants. SSL tissues show accumulation of butyltins, mercury, PCBs, DDTs, chlordanes and hexachlorobenzene. SSL habitats and prey are contaminated with additional chemicals including mirex, endrin, dieldrin, hexachlorocyclohexanes, tetrachlorodibenzo-p-dioxin (TCDD) and related compounds, cadmium and lead. In addition, many SSL haulouts and rookeries are located near other hazards including radioactivity, solvents, ordnance and chemical weapon dumps. PCB and DDT concentrations measured in a few SSL during the 1980s were the highest recorded for any Alaskan pinniped. Some contaminant exposures in SSL appear to be elevated in the Gulf of Alaska and Bering Sea compared to southeast Alaska, but there are insufficient data to evaluate geospatial relationships with any certainty. Based on very limited blubber data, current levels of PCBs may not pose a risk to SSL based on comparison to immunotoxicity tissue benchmarks, but SSL may have been at risk from pre-1990 PCB exposures. While exposure to PCBs and DDTs may be declining, SSL are likely exposed to a multitude of other contaminants that have not been monitored. The impacts of these exposures on SSL remain unknown because causal effects have not been established. Field studies with SSL have been limited in scope and have not yet linked contaminant exposures to adverse animal health or population effects. Several biomarkers may prove useful for monitoring exposure and additional research is needed to evaluate their utility in SSL. We conclude that there are insufficient data to reject the hypothesis that contaminants play a role in the continued decline of SSL, and suggest that a coordinated monitoring program be developed which can be related to key biological, ecological and laboratory toxicity data.     

Phthalates in indoor dust in Kuwait: implications for non‐dietary human exposure

Phthalates are semivolatile organic compounds with a ubiquitous environmental distribution. Their presence in indoor environments is linked to their use in a variety of consumer products such as children's toys, cosmetics, food packaging, flexible PVC flooring among others. The goal of this study was to investigate the occurrence and concentration of phthalates in dust from homes in Kuwait and to assess non‐dietary human exposure to these phthalates. Dust samples were randomly collected from 21 homes and analyzed for eight phthalates. The concentrations of total phthalates were log normally distributed and ranged from 470 to 7800 μg/g. Five phthalates [Di(2‐ethylhexyl) phthalate (DEHP), Di‐n‐octyl phthalate (DnOP), Di‐n‐butyl phthalate (DBP), Benzyl butyl phthalate (BzBP), and Dicyclohexyl phthalate (DcHP)] were routinely detected. The major phthalate compound was DEHP at a geometric mean concentration of 1704 μg/g (median, 2256 μg/g) accounting for 92% of the total phthalates measured. Using the measured concentrations and estimates of dust ingestion rates for children and adults, estimated human non‐dietary exposure based on median phthalate concentrations ranged from 938 ng/kg‐bd/day for adults to 13362 ng/kg‐bd/day for toddlers. The difference in exposure estimates between children and adults in this study supports previous reports that children are at greater risk from pollutants that accumulate indoors.     

Spatial variation of disinfection by-product concentrations: Exposure assessment implications

The use of public water system (PWS) average trihalomethane (THM) and haloacetic acid (HAA) concentrations as surrogates of “personal” exposures in epidemiological studies of disinfection by-products (DBPs) may result in exposure misclassification bias from various sources of measurement error including intra-system variation of DBPs. Using 2000–2004 data from 107 PWSs in Massachusetts, we assessed two approaches for characterizing DBP spatial variability by identifying PWSs with low spatial variability (LSV) and examining differences in LSV across DBP groups and by type of source water and primary disinfectant. We also used spatial differences to examine the association between THM concentrations and indices of social disadvantage; however, we found no correlations or statistically significant differences based on the available data. We observed similar patterns for the percentage of quarterly sampling dates with LSV across different types of source water for all DBPs but not across disinfectants. We found there was little overlap between sites classified as having LSV across different DBP groups. In the main analysis, we found moderate correlations between both approaches (φ_THM4 = 0.55; φ_BrTHM = 0.64; φ_HAA5 = 0.67); although Method 1 (based on concentration differences between samples) may be better suited for identifying PWSs for inclusion in epidemiological studies because it is more easily adapted to study-specific exposure gradients than Method 2 (based on categorical exposure percentiles). These data reinforce the need to consider different exposure assessment approaches when examining the spatial variation of multiple DBP surrogates as they can represent different DBP mixtures.     

Visually observed mold and moldy odor versus quantitatively measured microbial exposure in homes

The main study objective was to compare different methods for assessing mold exposure in conjunction with an epidemiologic study on the development of children's asthma. Homes of 184 children were assessed for mold by visual observations and dust sampling at child's age 1 (Year 1). Similar assessment supplemented with air sampling was conducted in Year 7. Samples were analyzed for endotoxin, (1-3)-β-D-glucan, and fungal spores. The Mold Specific Quantitative Polymerase Chain Reaction assay was used to analyze 36 mold species in dust samples, and the Environmental Relative Moldiness Index (ERMI) was calculated. Homes were categorized based on three criteria: 1) visible mold damage, 2) moldy odor, and 3) ERMI. Even for homes where families had not moved, Year 7 endotoxin and (1-3)-β-d-glucan exposures were significantly higher than those in Year 1 (p < 0.001), whereas no difference was seen for ERMI (p = 0.78). Microbial concentrations were not consistently associated with visible mold damage categories, but were consistently higher in homes with moldy odor and in homes that had high ERMI. Low correlations between results in air and dust samples indicate different types or durations of potential microbial exposures from dust vs. air. Future analysis will indicate which, if any, of the assessment methods is associated with the development of asthma.     

堆积碎石土斜坡浅表入渗的空间分布与变异性研究

为探究强降雨下堆积体斜坡入渗参数的空间分布与空间变异性,通过筛分试验及双环入渗试验分别对堆积体斜坡试验点不同粒径区间碎石质量分数、碎石土渗透系数、饱和渗透系数、不同深度碎石土含水率进行测量,对数据进行普通Kriging插值统计分析,运用交叉检验选定合理理论模型与参数,获得其空间分布与变异性特征。研究结果表明:测试区碎石土入渗符合Kostiakov模型;不同粒径区间碎石质量分数采用高斯半变异函数理论模型空间插值精度最高,碎石土渗透系数和不同深度碎石土含水率采用球状半变异函数理论模型空间插值精度最高;粒径大于10 mm碎石主要分布于坡顶与坡腰区域且使该区域碎石土渗透系数的空间变异性相对较大,细小碎石(粒径2~10 mm)则聚积在坡脚位置,碎石土渗透系数速率沿坡面由上至下呈逐渐减少的空间分布趋势;浅土层(0~15 cm)坡腰含水率比坡顶、坡脚要高,而深土层(15~25 cm)坡脚含水率比坡顶、坡腰要高,且随深度增加缓慢上升。研究结果可作为碎石土滑坡降雨致滑的理论参考依据。     

Spatial variability and source identification of rural precipitation chemistry in France

The precipitation chemistry in France has been examined for large-scale spatial variability using the MERA/WMO-GAW network of 13 rural sites equipped with wet-only collectors. Three classes of mean chemical compositions of MERA sites, corresponding to three different geographical regions in France have been identified by applying hierarchical clustering analysis. Factor analysis has also been performed on the deposition and concentration data sets for the three MERA sites. All the factors could be interpreted as falling into one of four categories: Acid, Sea, Neutralization, or an Agriculture/Soil association. Both sulfate and nitrate were found to be significant components of the acid factor for two stations (Morvan and Donon). These individual site analyses indicate that the sea has a strong influence on the precipitation chemistry at these continental stations. A comparison between factor analysis of concentrations and factor analyses of depositions suggests on the one hand that the acid forms, H₂SO₄ and HNO₃, seem preferentially present in cloud and on the other hand that the neutralization of precipitation acidity by soil-derived particles and by ammonia emissions seems to depend on the geographical and climatic characteristics of a site (altitude, proximity to human activity and precipitation amount).     

Seasonal variability in environmental tobacco smoke exposure in public housing developments

The risk of tobacco smoking and second‐hand smoke (SHS) exposure combined are the leading contributors to disease burden in high‐income countries. Recent studies and policies are focusing on reducing exposure to SHS in multiunit housing (MUH), especially public housing. We examined seasonal patterns of SHS levels within indoor common areas located on Boston Housing Authority (BHA) properties. We measured weekly integrated and continuous fine particulate matter (PM_2.5) and passive airborne nicotine in six buildings of varying building and occupant characteristics in summer 2012 and winter 2013. The average weekly indoor PM_2.5 concentration across all six developments was 9.2 μg/m³, higher during winter monitoring period (10.3 μg/m³) compared with summer (8.0 μg/m³). Airborne nicotine concentrations ranged from no detection to about 5000 ng/m³ (mean 311 ng/m³). Nicotine levels were significantly higher in the winter compared with summer (620 vs. 85 ng/m³; 95% CI: 72–998). Smoking‐related exposures within Boston public housing vary by season, building types, and resident smoking policy. Our results represent exposure disparities that may contribute to health disparities in low‐income communities and highlight the potential importance of efforts to mitigate SHS exposures during winter when outdoor–indoor exchange rates are low and smokers may tend to stay indoors. Our findings support the use of smoke‐free policy as an effective tool to eliminate SHS exposure and protect non‐smokers, especially residents of MUH.     

Spatial and inter-annual variability of specific sediment yield: case of hillside reservoirs in Central Tunisia

Water erosion is the major process responsible for soil loss in Central Tunisia. It represents a main risk of sedimentation which threatens the lifetime of water and soil conservation works in the region, such as hillside reservoirs. This paper focuses on the study of spatial and inter-annual variability of specific sediment yield (SSY) estimated from sediment yield (SY) of 23 small watersheds of hill reservoirs located in the Tunisian Dorsal and the Cap Bon regions. The calculated values of mean inter-annual specific sediment yield varied from 180 to 3298 t/km²/year, over a period of 12 years (from 1994 to 2006). The selected catchments were classified into three groups according to their SSY data. The SSY map, elaborated with a geographical information system (GIS), showed an important spatial variability between watersheds of the same group. Moreover, analyses of the coefficient of variation (CV) showed that 70% of the considered sites demonstrate a tendency to moderate and high inter-annual variability of SSY. In order to identify the principal factors governing variability of erosion and sedimentation, a multiple regression analysis was carried out using nine parameters characterizing morphology, topography, land cover, climate and protection works of the 23 considered sites. The generated model revealed that 85% of SSY variability is correlated to seven principal factors, which are drainage area (A), rainfall intensity recorded in 30 min (I ₃₀), percentage of water and soil conservation works, percentage of clay and carbonate in soils, vegetation land cover, overall slope index (I _G) and rainfall amount (R _a). The obtained SSY results were compared to others cited in a large bibliographical synthesis of studies carried out at the planet scale. We deduced that the SSY values obtained in this study are among the relatively high series in the world. The high variability of specific erosion rates in Central Tunisia is believed to be related to the semi-arid climate, characterized by the irregularity and the severity of storms and the spatial and temporal variability of other multiple factors affecting erosion processes.     

Reference method for the determination of beryllium in airborne particulates

A quantitative analytical method is described for the determination of beryllium in particulate air samples. The prepared sample is analyzed using atomic absorption in both the flame and flameless modes. Measurement is rapid and accurate. Possible interferences are discussed.     

Spatial variability of the characteristics of combined wet weather pollutant loads in Paris

An on-site observatory of urban pollutant loads in combined sewers has been created in Paris in order to investigate wet weather pollutant loads at different spatial scales. This observatory is composed of six urban catchments, covering areas from 41 to 2581ha. For a wide range of parameters including suspended solids (SS), volatile suspended solids (VSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), metals (Cd, Cu, Pb, Zn), aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (AHs and PAHs), this article serves to evaluate the potential scale effect on wet weather flow (WWF) quality. Although the extensive data set compiled herein has emphasized the high variability in WWF quality from one rain event to the next, no scale effect could be observed for a given rain event on pollutant concentrations, distributions between dissolved and particulate phases, pollutant contents and loads. Such results are of prime importance since they suggest (i) no spatial scale influence on WWF quality for the considered catchments and (ii) similar dominant sources and transfer processes at the various spatial scales.     

Spatial analysis of annual air pollution exposure and mortality

The aim of this study was to relate ambient air pollution levels to mortality in Auckland, New Zealand. We used urban airshed modelling and GIS-based techniques to quantify long-term exposure to ambient air pollution levels and associated mortality. After adjusting for age, sex, ethnicity, socio-economic status, and urban/rural domicile there was a 1.3% (95%CI: 1-1.5%) increase in non-external cause mortality, and 1.8% (95%CI: 1.5-2.1%) increase in circulatory and respiratory causes per 1 microg/m(3) increase in annual average NO(2). Based on these exposure-response relationships and applying an annual average threshold of 13 microg/m(3), the average annual (for 1996-1999) number of people estimated to die from non-external causes and circulatory and respiratory causes attributable to air pollution in Auckland is 268 (95% range: 227-310) (3.9% of total all cause deaths) and 203 (95% range: 169-237) (5.9% of total circulatory and respiratory deaths) per year, respectively. The number of attributable deaths found in this study are consistent with a previous New Zealand risk assessment using a different methodology, and is approximately twice the number of people dying from motor vehicle accidents in the region, which is on average (1996-1999) 103 per year. The GIS-based exposure maps identify high exposure areas for policy developers and planners in a simple and realistic manner. Taken together with overseas studies the study provides additional evidence that long-term exposure to poor air quality, even at levels below current standards, is a hazard to the public health.     

Soil salinity of urban turf areas irrigated with saline water: I. Spatial variability

With increasing use of saline water for irrigating urban landscapes, soil salinization is becoming a concern. This study examined spatial variation in soil salinity over the length of selected fairways at five golf courses, and of large turf areas at two public parks located in west Texas and southern New Mexico. Salinity of water used for irrigation ranged from 680 to 2700 mg L⁻¹, and the sites consisted mostly of Aridisols (upland soils) or Entisols (alluvial soils). Soil salinity distribution at sites consisting of deep Aridisols was spatially independent with the coefficient of variability (CV) ranging from 24 to 42%. The sites consisting of shallow Aridisols over a calcic horizon had erratic and random soil salinity distributions with an average CV of 37%. Since soil salinity distributions in Aridisols and Alfisols appeared to be spatially independent within the distance of fairways, soil sampling adequacy can be determined by the conventional probability statistics. However, salinity distributions at Entisols sites were spatially dependant to a length of 100 m or more. In addition, the clayey Entisols used for public parks had high levels of salt accumulation (>10 dS m⁻¹ in the saturation extract) with the CV exceeding 60%. When salinity readings were stratified by soil type distribution, the CV was reduced to 28% on the average. The number of samples required to obtain the mean salinity over a typical length of fairways (250–300 m) within a deviate range of 20% averaged 6 in deep sandy Aridisols and Alfisols, and 13 each in other cases, provided that sampling of Entisols is made based on soil type distributions. These sampling requirements are greater than those for field soil moisture or saturation water contents. The spacing to collect the required number of samples over the prevailing length of fairways was between 23 and 38 m. Soil sampling for salinity appraisal is most problematic in Entisols, but can be made simple if a detailed soil map is available. In Aridisols containing a calcic horizon, it is probable to have saline spots over poorly permeable caliche.     

Spatial and temporal variability in VOC levels within a commercial retail building

A study was performed to characterize the concentration of dozens of volatile organic compounds (VOCs) at 10 locations within a single large building and track these concentrations over a 2-year period. The study was performed at a shopping center (strip mall) in New Jersey. A total of 130 indoor air samples were collected from 10 retail stores within the shopping center and analyzed for 60 VOCs by US EPA Method TO-15. Indoor concentrations of up to 55,100 microg/m(3) were measured for individual VOCs. The indoor/outdoor ratio (I/O) was as high as 1500 for acetone and exceeded 100 at times for various compounds, indicating that significant indoor air sources were present. A large degree of spatial variability was observed between stores within the building, with concentrations varying by three to four orders of magnitude for some compounds. The spatial variability was dependent on the proximity of the sampling locations to the indoor sources. A large degree of temporal variability also was observed for compounds emitted from indoor sources, but the temporal variability generally did not exceed two standard deviations (sigma). For compounds not emitted from indoor sources at significant rates, both the spatial and temporal variability tended to range within an order of magnitude at each location. PRACTICAL IMPLICATIONS: Many cross-sectional studies have been published where the levels of volatile organic compounds (VOCs) were measured in indoor air at one or two locations for houses or offices. This study provides longitudinal data for a commercial retail building and also addresses spatial variability within the building. The data suggest that spatial and temporal variability are important considerations for compounds emitted from indoor sources. Elevated concentrations were found in retail spaces with no apparent emission sources due to their proximity to other retail spaces with emission sources.     

Spatial and temporal variability of priority volatile organic compounds in the Scheldt estuary

The occurrence and spatial-temporal variability of 25 volatile organic compounds (VOCs) was studied from May 1998 to November 2000 in the Scheldt estuary. Target VOCs were selected from lists of priority pollutants to the North Sea, and included chlorinated short-chain hydrocarbons (CHCs), monocyclic aromatic hydrocarbons (MAHs) and chlorinated monocyclic aromatic hydrocarbons (CMAHs). Samples were taken between Vlissingen and Temse over a 95 km trajectory, and analysed by purge-and-trap and high resolution gas chromatography-mass spectrometry. Data were attended by analyses deemed 'in control' by a rigorous quality assurance/quality control program, as proposed by Quality Assurance of Information for Marine Environmental Monitoring in Europe (QUASIMEME). CHCs were among the most commonly found VOCs in the estuary, ranging from a few ng l(-1) to several microg l(-1). Most analytes were traceable to a single input source in the upper part of the estuary, which is densely populated and highly industrialized. By contrast, the occurrence of MAHs resulted from contributions of a wide spectrum of sources. The CMAHs were less abundant in the water column, and were mainly detected as chlorobenzene and 1,4-dichlorobenzene. Concentrations of several priority VOCs have markedly decreased since 1995 owing to emission reduction efforts within international frameworks for the protection of the North Sea.     

Spatial variability of damage and expected maintenance costsfor deteriorating RC structures

The paper develops a technique to predict life-cycle costs, using probabilistic information about the likelihood and extent of corrosion-induced cracking to reinforced concrete (RC) structures. The present paper focuses on the likelihood and extent of severe cracking as the criterion for the timing and cost of maintenance. The life-cycle cost and expected maintenance cost considers multiple repairs and various inspection intervals over the service life of the structural element. A repair cost function is also developed. Two common maintenance strategies are considered: repair and rehabilitation. It was found that for a 2% discount rate the benefits of delaying the timing of repairs outweigh the cost of increased extent of damage, for maintenance of a RC bridge deck.     

Spatial and temporal variability in the structure of invertebrate assemblages in control stream mesocosms

Outdoor stream mesocosm studies conducted between 1992 and 1996 at two facilities enabled the investigation of structural variability in invertebrate assemblages within and between studies. Temporal variability of benthic invertebrate assemblages between eight replicate streams within a study was assessed in a 28-day mesocosm study without chemical treatment. Cluster analysis, non-metric multidimensional scaling, and principal component analysis each showed the untreated assemblages as structurally distinct groups on the three sampling days. The assemblages between the eight replicate streams showed >88% Bray-Curtis similarity at any one time during the study. In addition, pre-treatment data from a series of four studies conducted at one facility were used to examine structural variability in the starting benthic invertebrate assemblages between studies. Invertebrate assemblages were structurally distinct at the start of each mesocosm study conducted in different years at the same facility and the taxa responsible for differences in the assemblages were also different each year. The implications of temporal and spatial variability in benthic invertebrate assemblages within and between mesocosm studies with regards to species sensitivity and study repeatability should be considered when results of such studies are used in risk assessment.     

Spatial heterogeneity of personal exposure to airborne metals in French urban areas

The spatial distribution of urban population exposures to ambient air particles was investigated as part of the Genotox'ER study conducted in four metropolitan areas (Grenoble, Paris, Rouen and Strasbourg) in France. In each city, 60 to 90 non-smoking adult and children volunteers were selected. Subjects lived in three different urban sectors: one highly exposed to traffic emissions, one influenced by local industrial sources, and a background urban environment. The Harvard Chempass multi-pollutant personal sampler was used to sample PM10 and PM2.5 particles during 48 h during two different seasons ('hot' and 'cold'). The elemental composition of the filters was analysed by Particle-Induced X-ray Emission (PIXE). Sixteen elements were found to be over the method detection limits: Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn and Pb. The relative concentrations of elements of crustal origin (Si, Al, Ca) were higher in the coarse fraction of PM10 filters, while elements associated with combustion processes (traffic emissions or industrial combustion) presented higher relative concentrations in the PM2.5 fraction (S, Ni, V, Pb). Spatial heterogeneity of elemental exposures by urban sector is substantial for some metals of health concern, with 20% to 90% greater exposure values, on average, in the traffic proximity or industrial sectors, compared to the background sector, for Fe, Zn, Cu, V and Cr. This spatial heterogeneity should not be overlooked in epidemiological or risk assessment studies.     

The effects of human activities on natural radiation exposure: Health and regulatory implications

A decade ago, interest in “enhanced” natural radiation was focused primarily on localized industrial activities, e.g., uranium, radium, thorium and phosphate production. Recognition that all human activities influence natural radiation exposure, and that indoor radon exposure is particularly sensitive to such activities (building construction practice, occupant life-styles) has added a new dimension to the problem. Public health assessments must address the problem of high individual risks of lung cancer as well as substantial population risks that are only minimally ameliorated by reduction of high exposures. In the United States, Federal, State, and local government agencies are collaborating with the private sector in developing the information needed for public guidance. Voluntary standards relating to building construction practices are likely to be developed.     

Spatial and temporal variability of ribotyping results at a small watershed in South Carolina

The utility of library-based ribotyping methods for a very small study area was evaluated through comparison of local results to libraries with differing spatial and temporal scales. Ribotyping of Escherichia coli isolates was used to evaluate sources of fecal pollution at a coastal golf course in Beaufort County, South Carolina. Thirty-five E. coli isolates were obtained from water samples from a detention pond for testing against several local and regional libraries of known-source isolate patterns. A library of 92 E. coli ribotype patterns was created from wildlife feces obtained on the site. Additional libraries were available for comparison, including a library from Morgan Island, a small, geographically isolated area (including a monkey colony), and a library from ongoing statewide assessments. Seventeen (49%) of the unknown E. coli isolates matched isolates from raccoon and deer scat from the local library. Two isolates (6%) were matched with monkey sources from Morgan Island, and 13 (37%) were matched to raccoon, deer, and cows from the statewide assessment. Evaluation of repeated ribotyping analyses at the study area revealed evidence of temporal variability of potential sources in the local library. Only one of the isolates from the second year of fecal samples successfully matched with a fecal isolate from the previous year. The results from this study suggest that source identification results were variable both spatially and temporally, and that local, temporally specific libraries are most appropriate for library-based MST studies in small watersheds. Results also suggest that it will be difficult to employ adequate sample sizes to satisfactorily address unknown pattern variability.