Evaluation of dissipation mechanisms for pyrene by maize (Zea Mays L.) in cadmium co-contaminated soil

Sites co-contaminated with organic and metal pollutants are common and considered to be a
more complex problem, as the two components often have a synergistic effect on cytotoxicity.
This study investigated the dissipation mechnisms for pyrene in cadmium co-contaminated soil
in which maize (ZEA MAYS L.) was grown in a greenhouse experiment. Results showed the
growth response of maize may be affected by the co-contamination due to the interaction
between the heavy metal and organic pollutants. Pyrene in both planted and unplanted soil
diminished significantly at the end of 60-day culture, accounting for 21-31% of the initial
extractable concentration in unplanted soil and 12-27% in planted soil, which indicated that the
dissipation of pyrene was enhanced by the presence of vegetation. Although the presence of
cadmium stimulated the accumulation of pyrene in roots and shoots of maize, contributions of
plant off-take of pyrene to the total remediation enhancement in the presence of vegetation
was less than 0.3%. A significant positive correlation was observed between soil enzyme
activities (dehydrogenase, polyphenol oxidase) and the removal ratio of pyrene. Plant root
exudates appear to promote the number of rhizosphere microorganisms and enzyme activity,
thereby improving biodegradation of pyrene.