Heavy Metals Contamination In Xi’an City Suburb And Their Accumulation In Vegetables

The method of combining field investigation and indoor pot experiment wereadopted to study the heavy metal(Cd, Hg&As) contamination status of the soils andvegetables in the suburbs of Xi’an City and correlation analysis between heavy metalcontents of the soils and vegetables were made, the effect of soil physical andchemical properties on the vegetables’ absorption of heavy metals were discussed; theaccumulation characteristics of heavy metals in main varieties of green leafyvegetables were studied through pot experiment. The main results were as follows:1. The soil of Xi’an city suburb was slightly contaminated, in which Cd contentreached the slightly contaminated level while Hg and As content exceeded thewarning line. According to the comprehensive pollution index, the soil of WeiyangDistrict was moderately contaminated while the heavy metal contents of the soils ofLintong District and Baqiao District exceeded the warning line, soil pollution degreein different areas followed the order: Weiyang District＞Baqiao District＞LintongDistrict.2. On the whole, local vegetables were clean and safe. But some vegetables werecontaminated, nearly27.78%of the36vegetable samples’ Cd concentration exceededthe Cd criterion, and2.78%of the samples’ Hg concentration exceeded the Hgcriterion. Vegetable’ pollution degree in different areas followed the order: WeiyangDistrict＞Lintong District＞Baqiao District, while the heavy metal contents ofvegetables in Weiyang district exceeded the warning line. Pollution levels of differentvegetables were dufferent, while heavy metal contents of Brassica chinensis and Coleexceeded the warning line and Brassica pekinensis and Celery were safe.3. The Cd and Hg concentrations in vegetables were positively correlated to totaland available Cd and Hg concentrations in soil. Under pot experiment conditions, soilavailable heavy metal contents were positively correlated to that of the vegetablesexcept Hg content of Brassica pekinensis; after adding heavy metals to the soil, soiltotal and available Cd and Hg concentrations were positively correlated to that ofvegetables. 4. The enrichment capability of Cd and As in different vegetables followed theorder: Celery＞Cole＞Brassica chinensis＞Brassica pekinensis, and the enrichmentcapability of Hg followed the order: Celery＞Brassica pekinensis＞Cole＞Brassicachinensis. The accumulation potential of the3heavy metals in vegetables followedthe order: Cd＞Hg＞As. After adding heavy metals to the soil, the enrichmentcapability of Cd and Hg were bigger.5. Cd-Hg combined treatment could mitigate the inhibitory effect on the growth ofaerial parts of vegetables compared with Cd, Hg single treatment. Compared with Cdsingle treatment, Cd-Hg combined treatment reduced the accumulation of Cd in theaerial parts of Brassica chinensis while it promoted the absorption of Cd in aerial partsof Brassica pekinensis; compared with the Hg single treatment, the combinedtreatment reduced Hg accumulation in aerial parts of Brassica pekinensis under higherconcentrations6. An accidental contamination of higher concentration had a severe inhibitedeffect on the growth of the aerial parts of Brassica chinensis, whereas it promoted thatof Brassica pekinensis. The sprayed Hg of low concentration which lasted a long timeinhibited Hg absorption of the aerial parts of Brassica chinensis while it had apromoted effect on the Hg absorption of aerial parts of Brassica pekinensis, anaccidental higher concentration contamination greatly reduced the Hg content of theaerial parts of the two kinds of vegetables.