USE OF OCCUPATIONAL HYGIENE EXPOSURE DATA 601 Epidemiological study Ideally, occupational epidemiological studies should include exposure esti- mates of all employees to essentially all contaminants over all of the time period o f the study. Data on the degree of exposure will help the epide- miologist to identify a do se \200\223response relationship, which can aid the con- \201 rmation of a causal relatio nship between an agent and a disease. Various surrogates for exposure have also been used, such as job title, which is crude and can lead to misclassi \201 cation of employees and e xposure catego- ries. Retrospective exposure assessment can be impaired by recall bias, and by poor quality or missing data. Prospective exposure assessments may be hindered by data which is not representative of the whole study population. Monitoring the effectiveness of controls Control measures such as engineering need to be as sessed for their con- tinued effectiveness. This can be achieved by comparing the performan ce of the control measure against its design speci \201 cation e.g. for ventilation system s (velocities, pressure and \202 ow rates) or by monitoring changes in exposure level for the pollutant that the system is designed to control / minimize (see b Chapter 32). Informing the process of litigation Exposure data may be used in medico-legal cases. The re levance and reli- ability of the measured data may have an impact for both the plaintiff an d the defendant. 29_Smedley_Chap29.indd 601 1/2/2013 12:49:36 PM This page intentionally left blank 603 Chapter 30 Monitoring exposure Sample types for workplace pollutants 604 Selection of sampling and analysis methods 606 Wo rkplace exposure survey types 608 Exposure variability 610 Designing exposure monitoring pr ograms 612 Data interpretation 1: calculating TWA concentrations 614 Data interpretation 2: exposure to chemical mixtures 616 Dermal exposure 617 Conceptual model of dermal exposure 618 Dermal: exposure measurement and estimating uptake 620 30_Smedley_Chap30.indd 603 1/2/2013 12:51:24 PM CHAPTER 30 Monitoring exposure 604 Sample types for workplace pollutants Measurement of exposure in occupational hygiene norma lly involves col- lecting a sample from the breathing zone using personal sampling equip- m ent. However, in some cases air-sampling techniques alone may not provide a reliable indica tor of exposure, e.g. where there is potential for skin absorption or ingestion, or where R PE is used to control exposure (see b p. 652, Selecting respiratory equipment). Monitoring techniques Monitoring techniques for airborne pollutants can be divided into sev eral categories. \200 Instantaneous monitoring (direct reading): refers to the collection of samples, usually for a relatively short period. Instantaneous monitors may be used to detec t explosive concentrations of solvents, oxygen de \201 ciency, or physical hazards such as noise and light levels. The instrument may be linked to an alarm device or data downloaded to a computer to examine the exposure pro \201 le with time (see Fig. 30.1) \200 Integr ated monitoring: provides a single TWA concentration over a de \201 ned sampling period, i .e. averaging peaks and troughs, e.g. when sampling personal exposure to organic solvents u sing charcoal adsorbent tubes Personal sampling: involves the placement of a monitoring device within the individual \200 \231s \200\230breathing zone \200\231 (approximately 20 \200\22330cm from the nose/mouth) to sample the microenvironment from which the person breathes Static (area or \201 xed) samples: can be taken to check the effectiveness of process controls, to identify emission sources, to determine background concentrations i n the work environment (mapping), and in some cases as a surrogate for personal sampling Active and passive monitoring : active monitoring techniques involve use of a sampling pump to pull airborne pollutant through a sampling device, while the pass ive technique relies on molecular diffusion, e.g. diffusion badges Bulk samples: large volume of air, liquids, or settled particulates collected e.g. for qual itative analysis to determine the nature/ composition of pollutant. 30_Smedley_Chap30.indd 604 1/2/2013 12:51:24 PM SAMPLE TYPES FOR WORKPLACE POLLUTANTS 605 Fig 30.1 Video exposure monitoring. Combining a direct reading monitor with a video to exam ine the relationship between work practices and exposure. 30_Smedley_Chap30.indd 605 1/2/2013 12:51:24 PM CHAPTER 30 Monitoring exposure 606 Selection of sampling and analysis methods \200 Decisions on the selection of control mea sures frequently depend on measured exposure levels. Therefore, it is essential that measur ements are made using appropriate sampling and analytical methods The inherent limitations of the sampling and analysis methods used for data collection must be understood fully The objectives of the occupational hygiene survey and its design will help to de \201 ne t he acceptable accuracy, precision, and limit of detection for the pollutant(s) of interest Where available, standard methods of sampling and analysis should always be used. In the UK , sampling and analysis methods for a wide range of substances are detailed in the HSE MDHS series which are available on line at: M http://www.hse.gov.uk/pubns/mdhs \200 The Inter national Standard Organization (ISO), the European Committee for Standardization (CEN), and various national bodies, e.g. the US National Inst itute for Occupational Safety and Health (NIOSH), also publish methods for the measurement of workplace contaminants In the absence of a recommended reference sampling method, the following factors should be considered when selecting an appropriate method: \200 nature of the pollutants (gasses, vapors, mists, \201 bres, particles, etc.) to be collected and the stability of the sampling medium compatibility of the sampling medium with the subsequent analytical technique, e.g. GC, AAS, XRD capacity and collection ef \201 ciency of the sampling medium \200 intrinsic safety of t he sampling equipment, its ease of use, and portability for personal sampling. Analytical de \201 nition of terms \200 Speci \201 city: 1 the ability of the assay to measure one particular substance in the presence of another substance in the sample Sensitivity: 1 smallest amount of substance in a sample that can be accurately measured by an assay Accuracy : difference between the measurements and the true or correct value for the quantity measured Precision : closeness of agreement between the results obtained by applying the method seve ral times under prescribed conditions. Precision can be expressed by the standard deviation Limit of detection (LOD) : the smallest amount of a substance that can be reliably measured by the instrument which is distinguishable from the background. 1 3 The de \201 nitions of sensitivity and speci \201 city are those used in occupational hygiene practice and differ from those used in epidemiological surveys. 30_Smedley_Chap30.indd 606 1/2/2013 12:51:24 PM SELECTION OF SAMPLING AND ANALYSIS METHODS 607 Minimum sampling volume When sampling it is important to ensure that a suf \201 cient quan tity of sample is collected to enable the analyst (laboratory) to determine the amount of c ontaminant accurately. The minimum sampling volume (time) can be calculated from the follow ing equation: Min. sampling vol. (m 3 ) = (10 \227 LOD for analytical technique (mg)/OEL ( mg/m 3 )) Sampling and analysis errors and corrections When comparing measured exposure data with rel evant OELs it is impor- tant to consider the following: \200 Instrumental and analytical errors \200 Potential for contamination of sampling device \200 Sampling ef \201 cienc y of collecting devices and desorption ef \201 ciency of solid adsorbents Ensure that the measurements and OELs are expressed at standard temperature and pressure. F or example, as the exposure limits are based on a temperature of 20 C and a pressure of 76 0mmHg, the concentrations of any measured pollutant not measured at these values should be corrected as follows: C corr = C (760/ P ) ( T / 293) Where C corr is the corrected concentration, P (mmHg) is the actual pres- sure of air sampl es, and T (K) is the absolute temperature of air sampled. Quality assurance (laboratory analysis) When sending samples to analytical laboratories for analysis (after a expo- sure survey), e.g. analysis of sorbent tubes for solvents include: \200 \200\230Field blanks \200\231 for analysis. \200\230Field blanks \200\231 are sam ples taken to the worksite and treated and handled in the same way as other samples with the exception that n o air is drawn through the sampling media \200 Samples that are \200\230spiked \200\231 with a known amount of the substance(s) sampled in the workplace. - For information on practical methods for sampling hazards (chemical, physical, and biologic al agents) in the workplace, see Further reading. Further reading Cherrie J, Howie R, Semple S (2010). Monitoring for health hazards at work , 4th edn. Wiley- Blackwell, Oxford. 30_Smedley_Chap30.indd 607 1/2/2013 12:51:25 PM CHAPTER 30 Monitoring exposure 608 Workplace exposure survey types Three stages The design of the monitoring program will be s trongly in \202 uenced by the aim of the survey. The HSE has produced an outline for monit oring exposure, which includes three stages (initial appraisal, basic survey, and detailed survey). These are summarized here. The structured approach is summarized in Fig. 30.2. Initial appraisal This step helps to establish the need for, and the extent of, monitoring. Information is required on the following factors: \200 The substance to which individual s are exposed \200 The hazardous and physical properties of the substance \200 The airb orne form of the substance \200 The process or operations where exposure is likely to occ ur \200 The number, type, and position of sources from which the substance is released The groups of employees who are most likely to be exposed \200 The pattern and duration o f exposure, including exposure routes (inhalation, dermal, ingestion) Actual work practices \200 The means by which the release of the substance is controlled \200 Whether personal protective equipment is used and its effectiveness \200 The OELs for the substances involved. Basic survey This step involves identifying and monitoring exp osure of employees who are likely to be at signi \201 cant risk. Individuals at risk and p rocesses of con- cern are identi \201 ed using information collated in the initial apprais al, includ- ing situations when employees complain. The exposure is estimated using either semi-quantitative or validated laboratory-based samp ling and analysis methods. The survey also includes an indication of the ef \201 ciency of process and engineering controls. Detailed survey This is conducted when: \200 The extent and pattern of exposure cannot be con \201 dently assessed by a basic survey Exposure is highly variable between employees doing similar tasks \200 Carcinogenic subst ances (R45) or respiratory sensitizers (R42) are involved The initial appraisal and basic survey suggests that: TWA personal exposure may be very close to the OEL \200 costs of additional control measu res cannot be justi \201 ed without the evidence of the extent of exposure variability speci \201 c non-routine tasks are undertaken which require further investigation. 30_Smedley_Chap30.indd 608 1/2/2013 12:51:25 PM WORKPLACE EXPOSURE SURVEY TYPES 609 Prioritization of sampling needs Having determined the need and reasons for sampling, it ma y be necessary to make an a priori prioritization of contaminants and/or processes to be as sessed. The following factors should be considered when prioritizing sampling \200 Number of individuals potentially exposed to the substance \200 Toxicity of the substance(s) \200\224acute and chronic effects \200 Quantities (substance) used over some arbitrary re ference period \200 Pattern and estimate of exposure levels \200 Existence of, and con \201 dence in, control measures used to minimize exposure Reported symptoms \200 Findings from previous risk assessments. Start Initial appraisal what are the hazards & risks? Do you think exposure is under control? Yes No Basic survey Control the exposure Re-appraisal From the intial appraisal and basic survey decide if the level of risk is acceptable Routine monitoring No Need more information Yes Detailed survey From the monitoring results decide if the level of risk is acceptable Yes No Fig. 30.2 Structured approach for assessing exposure to substances hazardous to health (fro m HSE (1997). Monitoring strategies for toxic substances , HSG173. HSE Books, Sudbury. C rown copyright, reproduced with the permission of the Controller of HMSO. 30_Smedley_Chap30.indd 609 1/2/2013 12:51:25 PM CHAPTER 30 Monitoring exposure 610 Exposure variability Exposure to hazards (e.g. chemicals, noise, vibration.) in the workpla ce can vary both within and between individuals, days, shifts, etc. In order to obtain repr esentative exposure data for risk assessment these variables need to be understood and cons idered carefully in the design of occupa- tional hygiene sampling surveys. \200 Factors w hich in \202 uence the release and airborne concentrations of substances include: \200 physical and chemical properties of the substance \200 number of sources \200 rate, speed, and duration of release from each source \200 variation in the process, job, and tasks carried out \200 dispersion and mixing of agent in the workp lace \200 ambient work conditions (air movement, temperature, humidity) \200 Employees may in \202 uence the level and pattern of exposure by their individual work practice (pos ture, method of work) and attitudes towards risks (use of personal protective equipment) an d systems of work Identi \201 cation of variations of exposure within-days is of importance when the pollutant has potential to cause acute health effects Seasonal variations in exposure may occur due to differing production demands. It is important to document circumstances under which the exposure occurs. This information enables the interpretation of the data, and understanding the determinants of exposure and reasons for exposure variability. Table 30.1 lists the types of information to be collecte d during exposure measurement. 30_Smedley_Chap30.indd 610 1/2/2013 12:51:25 PM EXPOSURE VARIABILITY 611 Table 30.1 Information to be collected during exposure measurement Category Information Strategy Reason for collecting measurements Worst case or randomly chosen worker Task-speci \201 c or full-shift based Duration of sample Sampling and analytical method Location Type of industry Department Number of employees in the department Worker Personal identi \201 cation code Gender, age Worker behavior (e.g. tasks performed) Person al protective equipment used Machines and tools used Pace of work Degree of training Mobile or stationary work Process Level of automation Continuous or intermittent Control or exposure-reducing measures Environment Indoors or outdoors Temperature, atmospheric pressure, relative humidity Weather conditions (for outdoor work) Local and/or general ventilation Room volume (e.g. con \201 ned space <50m 3 ) Day or night shift Agents Likely source (e.g. composition of raw materials) Physical characteristics (e.g. particles, vapors, mists, \201 bres, etc.) Based on: Kromhout H (2002). Design of measurement strategies for workplace exposures. Occu p Environ Med , 59, 286, 349 \200\22354. 30_Smedley_Chap30.indd 611 1/2/2013 12:51:25 PM CHAPTER 30 Monitoring exposure 612 Designing exposure monitoring programs Occupational exposure monitoring programs should add ress the fol- lowing questions: \200 Whose exposure should be measured? \200 Where to c ollect the sample? \200 When to measure? \200 How long to sample? \200 Number of samp les? \200 How often? \200 How to interpret the data? When evaluating these questions, c onsider the following points: \200 For compliance purposes, sampling can be carried out o n a group basis where groups of employees are performing identical or similar tasks and are exposed to similar risks to health, i.e. homogenous groups. HSE (1989) states that if an i ndividual \200\231s exposure is less than half or more than twice the group mean, he/she sh ould be reassigned to another group For the assessment of human health risks personal sampling is preferred, as this is most likely to re \202 ect the individual \200\231s exposure. In fac t, for all, but a few substances (e.g. cotton dust, vinyl chloride monomer, and subtilisins (proteolytic enzymes)) the assigned OELs are speci \201 c to personal exposure When locating personal samplers consideration must be given to source(s) of exposure, work tasks, and individual work practices. Studies have shown up to twofold differences in dust level for samples placed equidistant from the nose/mouth on each lapel Start-up procedures at the beginning of the shift and end-of-shift procedures such as clean-down as well as unplanned events (chemical spillage) can make an i mportant contribution to daily exposures When sampling exposure to demonstrate compliance with OELs, the duration over which the sam ple should be taken is dictated by the reference period of the OEL. In the UK, OELs are exp ressed over two reference periods, i.e. 15min and 8h. Fig. 30.3 shows different sampling st rategies for obtaining 8h TWA concentrations Given the variability of occupational exposure data (see b p. 610), one or two samples take n on one day may be insuf \201 cient to reach reliable exposure estimates. The sample size requirements can be related to closeness of measured mean personal exposure levels to OEL for the contaminant of interest (Table 30.2) The decision on the frequency of monitoring should be based on factors such as reliability of controls, closeness of exposure levels with limits (Table 30 .3), changes in work practices, work equipment, work environment, and reported symptoms Exposure data is usually log normally distributed and can be expressed as a range, arithmet ic mean, geometric mean and geometric standard deviation or as a log probability plot to es timate percentiles points. 30_Smedley_Chap30.indd 612 1/2/2013 12:51:25 PM DESIGNING EXPOSURE MONITORING programs 613 Start shift Shift ends Fig. 30.3 Four different strategies for estimating the 8-h TWA concentration. Each offers d ifferent advantages and limitations. The arrowheads indicate the number of samples taken ov er the shift and their duration. Table 30.2 Sample size requirements for testing mean exposure from log normal distribution of 8-h TWAs (95% signi \201 cance and 90% power) Sample size n Mean/OEL SD = 1.5 SD = 2.0 SD = 2.5 SD = 3.0 SD = 3.5 0.1 2 6 13 21 30 0.25 3 10 19 30 43 05 7 21 41 67 96 0.75 2 82 164 266 384 1.25 25 82 164 266 384 1.50 7 21 41 67 96 2.00 2 6 11 17 24 3.00 SD, Geometric standard deviation. 1 2 3 5 6 Table 30.3 Minimum frequency of regular monitoring Shifts to be sampled (per 10 employees) Exposure/occupational exposure 1/month 1 \200\2232 1/fourth 0.5 \200\2231 or 2 \200\2234 1/annum 0.1 \200\2230.5 or 4 \200\22320 None <0.1 or >20 30_Smedley_Chap30.indd 613 1/2/2013 12:51:25 PM CHAPTER 30 Monitoring exposure 614 Data interpretation 1: calculating time-weighted average concentrations Air-borne concentra tions of substances are calculated using the following equation; C = M / V where C is the concentration (mg/m 3 ), M is the mass of substance (mg) and V the volume of air sampled (m 3 ). Calculating 8-h time-weighted average If exposure is measured by collecting a number of sam ples over an 8h period, then the 8h time-weighted average (TWA) is calculated by mul- tiply ing each exposure concentration by the corresponding exposure duration. 8h TWA = (C 1 x T 1 + C 2 x T 2 CnTn)/8 where C (mg/m 3 ) is the concentration and T the time (h). Example A machinist in a wood workshop works an eight hour shift. A personal sample was tak en using an IOM sampling head connected to a sampling pump for 2h. The sampling pump was ca librated at a \202 ow rate of 2.0L/min. The difference (gain) in the weight of the sampli ng \201 lter before and after sampling was 5mg. Personal sampling was conducted for two further periods on the same day, i.e. 2h and 4h whi ch produced TWA concentrations of 6.0 and 2.0mg/ m 3 , respectively. Question (a) What is the 2-h TWA personal dust concentration for the \201 rst sampling period? (b) What is the 8-h TWA? Calculation (a) 2h TWA = Mass(mg)/Vol. (m 3 ) 5.0mg/0.24m 3 21.0mg/m 3 (b) 8h TWA = (21.0 \227 2.0) + (6 \227 2) + (2.0 \227 4.0)= 8.0mg/m 3 Period of work >8h: adjustment of OEL \200 The use of unusual work schedules is now fairl y common. Consequently, workers will not experience occupational exposure over the traditional 8h per shift, 5 days a week, which is that used in setting OELs A work shift longer than 8h will result in additional exposure and also a shorter period of recovery before the next insult. This may not be a problem with substances with very short half-lives. However, the body burden for substances with half-lives approaching or exceedi ng 16h (the period of recovery for an 8h working day) may rise over the week/shift period 30_Smedley_Chap30.indd 614 1/2/2013 12:51:25 PM DATA INTERPRETATION 1 615 A number of sophisticated models utilizing pharmacokinetics have been put forward to adjust for exposures greater than the reference period of 8h. Unfortuna tely, they require a great deal of substance- speci \201 c information, which is very rare ly available. A more simplistic equation is given here which can be used to adjust the 8h O EL: OEL multiplication factor = 8/ H [(24 \210\222 H )/16] where H is the number of hours worked. 3 Note that the formula does not apply to continuous 24h exposure, work periods of <7 \200\2238h/day or 35h/wk, or concentration-dependent acut e toxicants. 30_Smedley_Chap30.indd 615 1/2/2013 12:51:26 PM CHAPTER 30 Monitoring exposure 616 Data interpretation 2: exposure to chemical mixtures Occupational exposure seldom involves exposure to a single substance. Exposure to mixtures is of concern in both measuring exposu re and estimating their biological signi \201 cance. Potential adverse effects may be grea ter than, less than, or equal to the sum of the effects of the individual components of the mixture. Evaluating exposure to mixtures \200 The majority of the substances encountered in occupa tional settings are assigned an individual WEL. Some WELs relate to substances commonly enc ountered as complex mixtures, e.g. welding, rubber, and solder fumes When individuals are exposed to mixtures, the \201 rst step is to ensure adequate control of each individual substance. It may then be necessary to assess wh ether further control is needed so as to counteract any increased risk due to presence of o ther substances in the mixture. Interaction should be considered in the following order: \200 synergistic effect \200\224occurs when the combined effect of the two agents is greater than the effect of each agent given alone. Antagonistic effects occur when the combined effect of two agents is less than the sum of the effects of each agent g iven separately additive effect \200\224is an example of a non-interaction, i.e. the combined effect of two agents is equal to the sum of the two effects of each agent given al one independent effects \200\224i.e. the other components do not add, enhance, or diminish the effect of the most active component, e.g. where each component act s on a different organ in the body and the magnitude of each effect is not in \202 uenced by the other effects When there is reason to believe that the effects of constituents are additive, and where th e WELs are based on the same health effects, the mixed exposure should be assessed using th e formula. C 1 / L 1 + C 2 / L 2 + C 3 / L 3 + < 1.0 where C 1 , C 2 , etc. are the airborne TWA concentrations and L 1 , L 2 , etc., are the co rresponding WELs. 30_Smedley_Chap30.indd 616 1/2/2013 12:51:26 PM DERMAL EXPOSURE 617 Dermal exposure Workers may be exposed to hazardous substances by inhalation, inges- tion, and contact with the skin or eyes. Exposure by the dermal route may result in local (skin i rritation, ulceration) as well systemic effects (neuro- toxicity, hepatotoxicity). \200 D ermal exposure occurs in a number of jobs, examples include: agricultural workers (pesticide sprayers) \200 painters (solvents) \200 hairdressers (d yes) \200 engineers (metalworking \202 uids) \200 construction workers (cements, solv ents, resins) \200 cleaners (solvents, skin irritants) Chemicals diffuse through the stratum corneum because of the concentration gradient between the skin contamination layer (SCL) (mixture of sweat, sebum, and other material on the skin) and the tissue around the peripheral blood supply Most gasses/vapors are not taken up by the skin in signi \201 cant quantities as the concentration gradient is too low The mass (surrogate for concentration) of a substance absorbed through the skin depends on the following properties of the substances, which are used to predict the permeability coef \201 cient of the substance ( K p): \200 solubility in oils and water \200 chemical s tructure \200 and molecular weight Dermal exposure assessment should include information on the following: \200 substance type \200 intensity (concentration or mass of substance on sk in) of exposure \200 duration and frequency of exposure High molecular weight liquids (>500Dal) with an octanol \200\223water partition coef \201 cient < \200\2231 or >4 are unlikely to permeate skin \200 Occlusion of the exposure site by clothing or personal protective equipment may i absorption through the skin. Skin notation \200\230Sk \200\231 Many national authorities publish occupational exposure limits and assign a \200\230skin notation \200\231 to substances when they judge that derm al exposure may make a signi \201 cant contribution to total exposure. List of chemicals ( more than 100) assigned \200\230skin notation \200\231 can be found in the HSE guide note EH40. Examples of Hazard Statements relevant to dermal exposure include H312 (harmful in contact with skin), H314 (causes severe skin burns), H315 (cause skin irritation), H317 (may cause an allergic skin reaction). See b Appendix 1 for health hazard statements. 30_Smedley_Chap30.indd 617 1/2/2013 12:51:26 PM CHAPTER 30 Monitoring exposure 618 Conceptual model of dermal exposure \200 Dermal exposure can be conceptualized according to a number of compartments and transfer routes (Fig. 30.4) Key transfer routes depend on the particular work situation, e.g. someone handling pesticide in a container may have direct splashes onto the SCL and the out er clothing contaminant layer from the source, together with direct contact of these layers with surfaces contaminated by pesticides Use of this conceptual model can help in the analysis of the main routes and compartments for different workplace exposure scenarios. Surface contamination layer Air compartment Source Outer clothing layer Inner clothing layer Skin contamination layer Fig. 30.4 Conceptual model of dermal exposure. 30_Smedley_Chap30.indd 618 1/2/2013 12:51:26 PM This page intentionally left blank CHAPTER 30 Monitoring exposure 620 Dermal: exposure measurement and estimating uptake Assessing the contribution of skin expos ure to systemic uptake Several methods are used to measure dermal exposure: \200 Intercep ting contaminants before they land on the SCL or clothing \200 Removal of contaminants fr om the SCL after exposure \200 In situ methods, e.g. use of \202 uorescent tracer compo unds. Qualitative assessment of dermal exposure To investigate skin exposure, collect good descri ptive information: \200 Record contact with contaminated surfaces (number of contacts, ar ea of SCL in contact, duration of each contact) Evidence of splash (liquids) or powder (solids) on surfaces \200 Large particles/droplets that may impact on worker or work surfaces \200 Type of clothing worn (note visible cont amination), glove type, whether gloves are worn continuously, reuse of gloves. 2 Videos are useful in analyzing worker behavior and dermal exposure. Interception methods Patch sampling \200 Widely used to sample low-volatility liquids, e. g. pesticides \200 Patches are attached to workers \200\231 clothing or the skin \200 P atches attached outside clothing are said to assess potential exposure \200 Samples insid e clothing are said to assess actual dermal exposure \200 Patches are analyzed to assess contaminant mass (and total body contaminant mass by multiplying the area of the body part by contaminant mass on the patch and summing overall). Suit sampling \200 An alternative interception sampler is the cotton \200\230suit sample r \200\231 \200 Suit analysis gives a direct estimate of whole-body contaminant mass landing on the SCL and/or clothing. Skin stripping \200 Skin stripping is a removal technique which can assess contaminant, e .g. acrylate, jet fuel, metal, that has started to permeate skin Adhesive tapes are used to remove ( \200\230strip \200\231) sequential layers of stratum corneum and any contaminant residues present in the skin. Removal techniques \200 Hand washing \200 Rinsing \200 Skin wiping. In situ methods \200 Fluorescent tracer methods are highly specialized research tools \200 Small amounts of a \202 uorescent agent are added to the contaminant source 30_Smedley_Chap30.indd 620 1/2/2013 12:51:26 PM DERMAL: EXPOSURE MEASUREMENT AND ESTIMATING UPTAKE 621 After work the skin is imaged with UV light using a video camera linked to a computer syste m to estimate tracer mass and hence contaminant mass. Biological monitoring and dermal exposure \200 Biological monitoring provides indirect as sessment of dermal exposure, but without exposure information it is of limited value \200 Biological monitor ing is often limited by availability of suitable method to measure the substance (parent co mpound or its metabolite) in the body Biological monitoring provides an assessment of PPE ef \201 cacy where data are available for workers with and without protective clothing. Surface monitoring \200 Surface contamination and transfer to skin play an important part in many dermal exposure situations (see Fig. 30.4) Surface contamination monitoring provides a measure of workplace contamination and its prob able contribution to dermal exposure \200 Surface wipe sampling is extensively used, but has high variability \200 Techniques are similar to those described for skin removal tech niques. Estimating dermal uptake The dermal uptake (mass) of a chemical can be estimated from the f ol- lowing equation: U sk = K p \227 C sk \227 A \227 t where K p is the permeability coef \201 cient (cm/h), C sk is the concentration of the sub stance on the skin (mg/cm 3 ); A is the area of skin exposed; t the duration of exposure (h ours). For a de \201 ned exposure scenario the relative uptake of a substance by both the dermal and inhalation route can be compared, i.e. contributions to total boy burden. The inhalatio n uptake ( U inh ) can be estimated from the following equation: U inh = C air \227 B \227 t where C air is the air concentration (mg/m 3 ); B the breathing rate (m3/h); t the exposure time (h). Further information Cherrie J, Howie R, Semple S (2010). Dermal and ingestion exposure meas urement In: Monitoring for health hazards at work , 4th edn. Wiley-Blackwell, Oxford. 30_Smedley_Chap30.indd 621 1/2/2013 12:51:26 PM This page intentionally left blank 623 Chapter 31 Biological monitoring Biological monitoring and biological effect monitoring 624 Interpretation of data 626 Pract ical and ethical considerations 630 31_Smedley_Chap31.indd 623 1/2/2013 12:52:50 PM CHAPTER 31 Biological monitoring 624 Biological monitoring and biological effect monitoring De \201 nitions Biological monitori ng The measurement and assessment of hazardous substances or their metabolites in tissue, s ecretions, excreta, expired air, or any combina- tion of these in exposed workers. Examples of blood and urine biological monitoring (BM) are shown in Table 31.1. Biological effect monitoring The measurement and assessment of a biological effect (early c onse- quences of exposure) in exposed workers, caused by absorption of chemicals. BM provides an indication of a workplace agent causing some detect- able biochemical altera tion. Unlike BM, biological effect monitoring BEM is not a surrogate of absorbed dose, but provides evidence of exposure. Examples of BEM include measuring the following biochemical responses: \200 Cholinesterase activity following an acute exposure to organophosphorus pesticides Urinary 2 -microglobulin proteins following exposure to cadmium \200 Free erythrocyte protoporphyrin (FEP) in blood or -aminolaevulinic acid (ALA-D) in urine for workers exposed to inorganic lead. Biological monitoring \200 Unlike air monitoring (external exposure) BM integrates exposu re received from all routes BM can be a useful complementary technique to air monitoring, particularly when exposure vi a the dermal route is signi \201 cant. Examples of chemicals which have the potential to p enetrate skin include those assigned the \200\230Sk \200\231 notation BM data can give useful information on the effectiveness of industrial hygiene controls, e. g. personal respiratory protective equipment as well as individual work practice BM sampling methods may be invasive and it may be dif \201 cult to distinguish between exposure at and away from work. 31_Smedley_Chap31.indd 624 1/2/2013 12:52:50 PM BIOLOGICAL MONITORING AND BIOLOGICAL EFFECT MONITORING 625 Table 31.1 Biological (blood and urine) samples and analytes Biological sample Example of parent compound Examples of metabolite Aromatic compounds: p henylmercapturic acid (for benzene), hippuric acid (for toluene), met hyl hippuric acids (for xylene), mandelic acid (for styrene and ethyl benzene), 1-hydroxypy rene (for PAHs) Urine Metals: mercury, lead (organic), cadmium, chromium, cobalt, vanadium Organic solvents: meth yl ethyl ketone (MEK), acetone, phenol, pentachlorophenol, 4,4 \200\231-methylene bis-2-cho roaniline (MbOCA) Chlorinated solvents: t richloroacetic acid (for trichloroethylene, perchloroethylene, 1,1, 1, trichloroethane) Other organic compounds: e .g. dialkylphosphates (for organophosphorous pesticides), 2,5-he xanedione (for n -hexane) Blood Metals: inorganic lead, mercury, cadmium, cobalt Organic solvents: aromatic compounds, e.g. toluene, styrene Chlorinated solvents: trichloroethylene, tetrachloroethylene, 1,1,1 trich loroethylene, Inorganic gasses and chlorinated solvents: c arboxyhaemoglobin (for methylene chloride and carbon monoxide), trichloroethanol (for trichloroethylene) 31_Smedley_Chap31.indd 625 1/2/2013 12:52:50 PM CHAPTER 31 Biological monitoring 626 Interpretation of data Units and creatinine correction \200 Blood samples: in micrograms ( g) or milligrams per liter (mg/L). \200 Urine levels: in milligrams per gram (mg/g) of creatinine, or millimoles per millimole (mmol/mmol) of creatinine. Urine concentration c an vary widely because of variation in \202 uid intake and sweat. Concentration/ dilution effects are corrected by adjusting for speci \201 c gravity or creatinine correction. Cre atinine correction is not advised if the creatinine <3 or >30mmol/L. Biological exposure limits BM data are usually compared with biological exposure standards set by national authorities. Examples include the following: \200 The TLV list of the ACGIH contains Biological Exposure Indices (BEIs ). 1 The BEI are advisory referen ce values and represent the concentration of a substance that is likely to be found in the sample of a worker who was exposed through inhalation to the TLV . The Deutsche Forschungsgemeinschaft (DFG, the German Research Foundation) publishes an annu al list of biological tolerance values (BAT). A BAT is de \201 ned as a maximum permissibl e quantity of a substance which does not generally impair the health of a worker. Thus the BAT value is primarily health based. In the UK there is a statutory requirement for monitoring lead under the CLAW Regulations. Under CLAW, action and suspension levels are assigned for lead workers. However, for other substances hazardous to health the HSE has adopted non-statutor y biological monitoring guidance values (BMGVs). Biological monitoring guidance values \200 BMGVs are non-statutory. Where the BMGVs are e xceeded, this indicates that work practices and controls need to be investigated. It does n ot imply that health effects will occur or that the WEL is exceeded. Table 31.2 gives a lis t of chemicals and their assigned BMGV values. For each substance, a free lea \202 et is a vailable from the HSE describing the analytical method, sampling strategy, quality assuranc e schemes, and interpretation of results BMGVs for different substances may be based on different information types which may include one of the following: \200 relationship between biological concen trations and health effects \200 relationship between biological concentrations and expos ure at the level of the workplace exposure limit (WEL) or data collected from representative samples of workplaces that are using principles of good occupational hygiene practice to minimize exposure. 1 ACGIH (2011). Threshold Limit Values for Chemical Substances and Physical agents & Biolog ical Exposure Indices . ACGIH, Cincinnati. 31_Smedley_Chap31.indd 626 1/2/2013 12:52:50 PM INTERPRETATION OF DATA 627 Table 31.2 BMGV values Substance BMGV Sampling time Butan-2-one 70 mol butan-2-one/Lin urine Post-shift 2-Butoxyethanol 240mmol butoxyacetic acid/ mol creatinine in urine Post-shift Carbon monoxide 30ppm carbon monoxide in end-tidal breath Post-shift Chromium VI 10 mol chromium/mol creatinine in urine Post-shift Cyclohexanone 2mmol cyclohexanol/mol creatinine in urine Post-shift Dichloromethane 30ppm carbon monoxide in end-tidal breath Post-shift N , N -dimetylacetamide 100mmol N -methylacetamide/ Post-shift mol creatinine in urine Glycerol trinitrate 15 mol total nitroglycols/mol creatinine in urine At the end of the period of exposure Lindane 35nmol/L (10 g/L) of lindane in whole blood (equivalent to 70nmol/L of lindane in plasma) Random MbOCA 15 mol total MbOCA/mol creatinine in urine Post-shift Mercury 20 mol/mol creatinine in urine Random 4-Methylpentan-2- one 20 mol 4-methyl pentan-2- one/L in urine Post-shift 4,4 -Methylene dianiline (MDA) 50 mol total MDA/mol creatinine in urine Post-shift for inhalation and pre-shift next day for dermal exposure Polyaromatic hydrocarbons (PAHs) 4 mol 1-hydroxypyrene/mol creatinine in urine Post-shift Xylene, o-, m -, p -, or mixed isomers 650mmol methyl hippuric acid/mol creatinine in urine Post-shift Crown copyright, material is reproduced with the permission of the Controller of HMSO an d Queen \200\231s Printer for Scotland. 31_Smedley_Chap31.indd 627