New Model for Biological Monitoring of Occupational Chemical Exposure to Volatile Organic Compounds

Introduction
We have tested (2006-2010) a New Model in the Practice of Biological Monitoring of Occupational Chemical Exposure to Volatile Organic Compounds (VOCs) as benzene, toluene, xylene, styrene and ethylbenzene in 5,347 urine samples from workers at risk of occupational exposure in Petrochemical Plants and Oil Refineries of the Mexican Petroleum Industry, in order to improve environmental work conditions.

Methods
Considering the biological half live of the main VOC's metabolites is between 1.5 h and 6 h, and the low or medium specificity and sensitivity of some metabolites, and the difficult assessment of contaminants exposure at work, we performed a systematic collection of Urinary Control Samples of each worker before the shift to evaluate the recent body burden of non-occupational exposure, this is because active and passive smoking, diet and medication may contribute to the toxicants body burden. For this purpose, we analyzed phenols, hyppuric acid, methyl-hyppuric acids, mandelic acid and phenylglyoxylic acid as biomarkers for benzene, toluene, xylene, styrene and ethylbenzene respectively. As an integral part of this model, we applied two questionnaires individually, one before the shift to identify confusion factors related to non-occupational exposure and the other at the end of shift that points out industrial hygiene conditions. Over-exposed workers with low biomarkers concentrations in their control samples and high concentrations in samples collected at the end of shift are subjected to a Follow up Biomonitoring program.

Results
Urinary Control Samples allows to discard non-occupational exposure, identifying workers already exposed previous to their work shift. Follow up biomonitoring allows an efficient control and prevention of exposure to chemical toxicants in over exposed workers by the application of some industrial hygiene measures like personal protective equipment.

Discussion
The routinary application of this new model allows to obtain more precise and exact results in the biomonitoring of occupational chemical exposure.