Removal of benzene by the indoor plant/substrate microcosm and implications for air quality

The quality of the indoor environment has become a major health consideration, since urban-dwellers spend 80-90% of their time indoors, where air pollution can be several times higher than outdoors. 'Indoor' potted-plants can remove air-borne contaminants such as volatile organic compounds (VOCs), over 300 of which have been identified in indoor air. In this study a comparison was made of rates of removal of benzene, as model VOC, by seven potted-plant species/varieties. In static test-chambers, high air-borne doses of benzene were removed within 24 h, once the response had been stimulated ('induced') by an initial dose. Removal rates per pot ranged from 12-27 ppm d(-1) (40 to 88 mg m(-3) d(-1)) (2.5 to 5 times the Australian maximum allowable occupational level). Rates were maintained in light or dark, and rose about linearly with increased dose. Rate comparisons were also made on other plant parameters. Micro-organisms of the potting mix rhizosphere were shown to be the main agents of removal. These studies are the first demonstration of soil microbial VOC degradation from the gaseous phase. With some species the plant also made a measurable contribution to removal rates. The results are consistent with known, mutually supportive plant/soil-micro-organism interactions, and developments in microbially-based 'biofilter reactors' for cleaning VOC-contaminated air. The findings demonstrate the capacity of the potted-plant microcosm to contribute to cleaner indoor air, and lay the foundation for the development of the plant/substrate system as a complementary biofiltration system.