Potential for Transfer of Lead, Arsenic and Polycyclic Aromatic Hydrocarbons From Compost Added Urban Soils to Vegetables and Humans.

Lead (Pb), arsenic (As) and polycyclic aromatic hydrocarbons (PAHs) are some of the most common soil contaminants in urban gardens. Therefore, they have potential to cause health problems to humans by soil ingestion and vegetable consumption. We compared effectiveness of four compost types (composted biosolids, Carmel biosolids, mushroom compost and leaf compost) with contrasting origin and/or maturity on reducing bioavailability of these contaminants using a field experiment conducted in Indianapolis, IN. Rate of compost addition was 44 kg/m². Collard greens, carrot and tomato were grown in the plots. Collard greens were cleaned using two cleaning techniques: 1) Lab cleaning:  using sodium lauryl sulphate and distilled water 2) Kitchen cleaning: using distilled water. Average Pb concentration in the soil was 467.7±23.9 mg/kg and As concentration was 48.1±0.9 mg/kg. Benzo(b)fluoranthene was the PAH that had the highest concentration (18.7 mg/kg). Concentration of benzo(a)pyrene in the soils ranged from 1.4 to 9.9 mg/kg.  Addition of compost diluted soil total Pb concentration by 57 to 19% and total As concentration by 51 to 10%.  Lead concentrations in collard greens were not statistically different among the treatments.  Proportion of soil Pb concentration that transferred to collard greens (i.e. bioconcentration factor) was higher in composted biosolids applied soils compared to that of the other treatments.. The bioconcentration factor of collard greens that were grown in the other compost applied and the control plots were not statistically different. Lead concentration in laboratory cleaned collard greens was lower than kitchen cleaned collard greens. Concentrations of PAHs in tomato and carrot were below the method detection limits (0.01mg/kg for less than 5 rings PAHs, 0.04 or 0.1 mg/kg for 5 and 6 rings PAHs).  Concentrations of Pb and As in all three vegetables and bioaccessiblity of Pb and As in soils (by an In vitro test) will be presented.