A comparison of metal average concentration (mg kg−1) in street dust from some cities.

a[22].b[21].c[44].d[24].e[50].f[51].g[43] Environmental quality standard for soils in China (National Environmental Protection Agency of China, 1995), and values in Class I are threshold levels of nationwide natural background.h[43] Values in Class II are threshold values established to protect agricultural production and maintain human health.i[43] Values in Class III are estalbished to maintain normal growth of plants, particularly the trees.

a[22].b[21].c[44].d[24].e[50].f[51].g[43] 中国土壤环境质量标准（Environmental quality standard for soils in China）由原中国国家环境保护总局（National Environmental Protection Agency of China）于1995年颁布，其Ⅰ类标准值为全国自然背景的阈值水平。
h[43] Ⅱ类标准值为保护农业生产、维护人体健康所设定的阈值。
i[43] Ⅲ类标准值为保障植物（尤其树木）正常生长而制定的标准。