Environmental effect of Sudan I-IV: adsorption behaviors and potential risk on soil

Sudan dyes (Table 1) [1], a class of synthetic azo dyes and classified as category 3 carcinogens by the International Agency for Research on Cancer[2], have been received considerable attention all over the world, especially in the past decade, which are found to be non-authorized and illegally added into food products, such as chili-, curry-, curcuma- and palm oil-containing foodstuffs, meats, spice mix, as well as feedstuffs and feed poultry, to enhance or maintain the appearance due to their intensive color and low price[3,4]. In addition, they are extensively applied in industrial and scientific areas, such as oils, textiles, plastics, waxes, inks, films, cosmetic products, shoe and floor polishing, and spirit varnishing[5-7]. Obviously, there exist a variety of potential sources for environmental contamination by Sudan dyes, thus threatening human health and the safety of ecosystems. It is reported that sub parts per billion levels of Sudan dyes were present in paprika fruits during the vegetation process, particularly, Sudan I existed in almost all samples, including paprika fruits, soils and agronomic materials from some fields in China[8],the levels in soils were significantly elevated by vegetation treatments, and pesticides and fertilizers constitute the major source of Sudan I contamination[9]. Till now, the investigation on contaminative behavior and environmental effects is rarely involved, and biogeochemical cycles of Sudan dyes are rarely concerned either.