Budget of Heavy Metals in Small-Sized Vegetable Farming System in a Typical Peri-Urban Agricultural Area

Urban Farm DB summary

A study of a small-scale vegetable farming system in peri-urban Nanjing, China, monitored heavy metal balances and pollution potential from July 2003 to July 2004. Heavy metals entered the soil mainly through fertilization and irrigation, with organic manure application accounting for more than 98% of inputs. Annual heavy metal input in the area was significantly higher than in European farmland, while annual output was very low, under 10% of input, leading to accumulation of heavy metals in the plots; long-term vegetable cultivation had already caused heavy metal buildup in the soils. Copper, lead, zinc, and cadmium concentrations in vegetables and soil were still below national safety standard limits, so the vegetable farming system was assessed as currently safe. However, an evaluation that incorporated atmospheric deposition showed the region carries a high risk of copper, zinc, and cadmium contamination, and the study concludes that intensive vegetable cultivation will aggravate soil heavy metal pollution, potentially pushing the soil to Second Grade of the National Soil Environment Quality Standard within several decades.