Effects of roadside dust on seed germination and root growth of Brassica chinensis and B. parachinensis

The roadside dusts collected from two selected sites, Ting Kok and Tai Po Road, with marked differences in Annual Average Daily Traffic value (AADT of Tai Po - 27990, Ting Kok Road - 16040) were passed through a 125 μm sieve and analysed for copper, lead, manganese and zinc. The concentration of each metal has been determined both as the total, extractable and water-soluble fraction, using mixed acid, 1M NH₄OAc (pH 7.0) and distilled water, respectively. It was found that the lead and zinc contents of the Tai Po site were higher than those of the Ting Kok site. Different concentrations (5%, 10%, 20% & 30% w/v) of water extracts of roadside dust from the two sites were used to study their effects on seed germination and root growth of two vegetable crops, Brassica chinensis and B. parachinensis. There was no marked effect on seed germination for different concentrations on the two vegetable crops of dust extracts from both sites. On the other hand, higher concentrations of dust extracts from the Tai Po site caused marked reduction of root growth for both crops but the effect on B. parachinensis was less obvious than on Brassica chinensis. Moreover, the dust extracts from the Ting Kok site enhanced the root growth of B. chinensis which may possibly be due to the fertile soil particles deposited from the nearby agricultural areas, resulting in higher contents of nitrogen and phosphorus as indicated in the analsis of dust extracts.