Enrichment amounts of arsanilic acid in livestock manure affect plant growth development and alter accumulation profiles of arsenic in rice

Objectives Arsanilic acid (AA) has been widely applied as feeding stuff additives in livestock and poultry breeding. These organic arsenic compounds are not easily absorbed in the intestinal system of animals, and usually excrete with manure in an original form. Therefore, application of such manures exerts negative effects on crop growth and development, and endangering human health through food chains.

Methods A pot experiment was conducted using rice and cinnamon soil as tested materials. A certain amounts of arsanilic acid were added into dry manures, and then the manures were applied in rate of 22 t/hm² into soils to make treatments of arsanilic acid levels of 0, 30, 75 and 150 mg/kg in soils, with soil applying no arsanilic acid polluted manure as control. The plant samples at tillering and flowering stages were divided into roots, stems and leaves, and the samples at maturating stage were divided into roots, stems, leaves, husks, brown and polished rice, the arsenic contents and cumulative amounts were analyzed.

Results Compared with the control, the root length, root number per plant and plant height were not significantly affected in treatments of AA 30–150 mg/kg, the ineffective tillers were significantly increased at AA 150 mg/kg, the grain yields were significantly decreased at the AA 75 and 150 mg/kg. The shoot biomass in the treatment of AA 150 mg/kg was remarkably higher than those in AA 0 and 30 mg/kg (P < 0.05), and the number of ineffective tillers in the treatment of AA 150 mg/kg was significantly increased (P < 0.05). The arsenic contents in rice roots, stems and leaves of all the AA treatments were significantly increased at all the sampling stages (P < 0.05). Compared with AA 30 mg/kg, the arsenic contents in rice roots in AA 150 mg/kg were significantly increased by 40.5% at tillering stage, 46.2% at flowering, and 53.1% at mature stage (P < 0.05), respectively; the arsenic contents in stems and leaves in AA 150 mg/kg were significantly increased by 56.1% and 30.9% at flowering stage, 86.7% and 61.8% at mature period (P < 0.05), respectively. The arsenic content in rice roots in AA treatments exhibited the highest enrichment at flowering stage, and started decreasing at mature stage. When the AA level was ≤75 mg/kg, the arsenic content in rice stems and leaves reached the highest at flowering stage and declined at mature stage. When AA treatment was 150 mg/kg, the arsenic contents in rice stems and leaves at maturity stage were the highest, and then were at flowering and tillering stages in turn. Relative to the control, the arsenic contents in rice grain of all AA treatments were significantly increased (P < 0.05). Compared with AA 30 mg/kg, the arsenic contents in husks and brown rice in AA 75 mg/kg were significantly increased by 138.5% and 126.1%, respectively, and the those in glumes, rice husk, brown and polished rice in AA 150 mg/kg were significantly increased by 24.6%, 165.7%, 158.7% and 125.0%, respectively.

Conclusions When applying compost containing arsanilic acid, the application levels of arsanilic acid in soil should be controlled not exceeding 75 mg/kg in cinnamon soil, otherwise will trigger toxic detriment to rice, and increase the risk of arsenic pollution in edible grain.