Ash and biochar mixed biomixtures to degrade co-applied atrazine and fipronil in bio-augmented biobeds

Abstract

ABSTRACT Retention and degradation of co-applied atrazine and fipronil was studied in laboratory constructed bio-augmented biobeds containing rice straw-compost (BM) and compost replaced with 10% rice husk ash [RHABM(10%)] or 1% wheat straw biochar [WBCBM(1%)] biomixtures. Atrazine (5000 µg, 50% WP) and fipronil (5000 µg, 0.3 G) were co-applied in 100 mL water. After 30 days, 7.31, 4.65, and 11.21 µg g−1 atrazine and 21.59, 7.41, and 37.20 µg g−1 fipronil remained undegraded in the top 3–4 cm of BM, RHABM(10%), WBCBM(1%) biobeds, respectively, suggesting that degradation of both pesticides significantly varied (p < 0.05) among the three biobeds. After 60 days 94.5%–98.3% of initially applied atrazine and 80.3%–86.9% fipronil degradation was observed. Hydroxyatrazine and sulphone were detected as the metabolites of atrazine and fipronil, respectively. Out of 5000 µg of initially applied pesticides, BM, RHABM(10%), and WBCBM(1%) biobeds accounted for 95.2%, 93.1%, and 95.2% of atrazine + hydroxyatrazine and 62.8%, 67.0%, and 71.5% of fipronil + sulphone degradation, respectively. Maximum amounts of recovered atrazine (68.8%–81.1%) and fipronil (89.8%–94.6%) were retained in the 0–5 cm sections of the biobeds. No significant effect of co-applied atrazine + fipronil was evident on the microbial parameters. This study suggested that RHA/WBC-mixed rice straw-compost biomixtures can be exploited for the detoxification of these pesticides in bio-purification systems.