Samples of vegetables available in some Delhi markets have been found to be contaminated with pesticide residue and heavy metals like zinc, lead and cadmium, Lok Sabha was informed. A study of 4,100 samples of 31 vegetables found 55 of them to be contaminated with pesticide residues, but only nine per cent of them exceeded the maximum residue limit, Agriculture Minister Ajit Singh said during question hour. The main reasons for heavy metal accumulation in vegetables were irrigation with sewage water and industrial effluents. Aerial deposition from thermal plants and vehicular exhaust were other major sources of heavy metals, he said.