Effective Factors on Determination of Hexavalent Chromium in Air

Introduction: In electroplating processes, hexavalent chromium mist is emitted in air. Hexavalent chromium mist can cause lung cancer and nasal septum in workers. As Permissible Exposure Limit (PEL) of hexavalent chromium is low (0.5 µg/m³) and it is used in various industries, evaluation of workers exposure to hexavalent chromium is very important. However, hexavalent chromium is relatively unstable and it can be reduced to trivalent chromium during sampling, storage, and extraction. So, factors influencing determination of Cr (VI) must be evaluated. In this study, influence of some factors such as sampling time, storage time, type of filter, and storage temperature on reduction of Cr (VI) were investigated.

Materials and Methods: In this study, based on experimental design, 168 hexavalent chromium mist samples were collected and analyzed according to the NIOSH 7600 method. All samples were collected by two types of filters (PVC, BQFF) at different sampling durations (30, 180, 480 min) and different storage times (0, 3, 24, 72 hours). Some samples were analyzed immediately after sampling and some of them were stored at 3, 24, and 72 hours at two different temperatures (20-25^°C, 4^°C).

Results: Results showed that, Cr (VI) concentration was decreased with increasing the sampling time (P_value<0.001), also, Cr (VI)^{concentration was decreased gradually with increasing of storage duration (P_value< 0.001). Hexavalent chromium mean concentration in BQFF filter was more than PVC filter (P_value<0.001). Also, storage temperatures had no effect on reduction of} Cr (VI) (P_value>0.05)

 Conclusion: Because of acidic and instability of Cr (VI) mist air, by increasing sampling time, Cr (VI) is reduced. Also, acidic media of filter at sample storage can cause possible reaction of polymeric and oligomer materials of filter media with Cr (VI), in which, with increasing storage time, Cr (VI) can be reduced on filters. On the whole, at starting sampling times (30 min) BQFF is more efficient than PVC for collection of Cr (VI). Based on the obtained results, storage conditions of samples had no effect on Cr (VI) reduction.