text: The direct approach measures the exposures to pollutants by monitoring the pollutant concentrations reaching the respondents.  The pollutant concentrations are directly monitored on or within the person through point of contact, biological monitoring, or biomarkers.  In a workplace setting, methods of workplace exposure monitoring are used.
  The point of contact approach indicates the total concentration reaching the host, while biological monitoring and the use of biomarkers infer the dosage of the pollutant through the determination of the body burden. The respondents often record their daily activities and locations during the measurement of the pollutants to identify the potential sources, microenvironments, or human activities contributing the pollutant exposure.  An advantage of the direct approach is that the exposures through multiple media (air, soil, water, food, etc.) are accounted for through one study technique. The disadvantages include the invasive nature of the data collection and associated costs.  Point of contact is continuous measure of the contaminant reaching the target through all routes.
  Biological monitoring is another approach to measuring exposure measures the amount of a pollutant within body tissues or fluids (such as blood or urine). Biological monitoring measures the body burden of a pollutant but not the source from whence it came. The substance measured may be either the contaminant itself or a biomarker which is specific to and indicative of an exposure to the contaminant. Biomarkers of exposure assessment is a measure of the contaminant or other proportionally related variable in the body.
  Air sampling measures the contaminant in the air as concentration units of ppmv (parts per million by volume), mg/m (milligrams per cubic meter) or other mass per unit volume of air.  Samplers can be worn by workers or researchers to estimate concentrations found in the breathing zone (personal) or samples collected in general areas can be used to estimate human exposure by integrating time and activity patterns.  Validated and semi-validated air sampling methods are published by NIOSH, OSHA, ISO and other bodies.
  Surface or dermal sampling measures of the contaminant on touchable surfaces or on skin.  Concentrations are typically reported in mass per unit surface area such as mg/100 cm.
  In general, direct methods tend to be more accurate but more costly in terms of resources and demands placed on the subject being measured and may not always be feasible, especially for a population exposure study.
  Examples of direct methods include air sampling though a personal portable pump, split food samples, hand rinses, breath samples or blood samples.