uptake and removal capability of toxic heavy metals from the industrial discharge of mobarakeh steel complex by metal accumulating plants

introduction heavy metals are largely found in dispersed form in rock formations. industrialization and urbanization have increased the anthropogenic contribution of heavy metals in the biosphere. heavy metal pollution not only affects the production and the quality of crops, but also influences the quality of the atmosphere and water bodies, and threatens the health and life of human beings. clean-up technologies have been developed for the removal of heavy metals but often these are expensive or have some environmentally deleterious consequences. phytoremediation emerged in the early 1980s is an important technology for remediation of contaminated sites. one of the most promising phytoremediation technologies is phytoextraction using hyperaccumulators to remove heavy metals from contaminated soils. however, the known hyperaccumulator plants usually accumulate only a specific element and are usually small. recently, most attention is focused to the plants that produce high biomass and are tolerant to the soils pollutted with heavy metals. t. caerulescens was found to colonize areas with high cd, cu, pb, and zn present in soils due to mining. m. chenopodiifolia has good potential for absorbing pb and zn. eruca sativa is tolerante to soil pollution with heavy metals and can accumulate pb and cd from contaminated soils. b. napus accumulated cadmium and zinc and translocated these elements into the harvestable parts of the plant. s. nigrum is often found in contaminated areas. it has previously been identified as a cd hyperaccumulator. h. annuus is known for its high biomass yield. in addition, it is tolerant to soil pollution with heavy metals. z. mays produce high biomass as well. in this study, we studied the capability of stability, growth, and uptake of heavy metals by means of t. caerulescen, z. mays, h. annuus, e. sativa, b. napus, s. nigrum, and m. chenopodiifolia on the industrial discharge of mobarakeh steel complex.   materials and methods mobarakeh steel company is located 75 km south west of isfahan, near the city of mobarakeh, isfahan province, iran. it is iran's largest steel maker and one of the largest industrial complexes operating in iran. three type effluents (first and second type and galvanized unit) were taken from separated lagoons. the ph of the soil was determined using a glass electrode after 10 g of soil had been stirred well in 30 ml distilled water in a beaker and allowed to stand for about 30 min. in the first experiment, pots (9 cm diameter) fill up with the first and second types and the galvanized unit effluents separately. the seeds of each plant (t. caerulescen, z. mays, h. annuus, e. sativa, b. napus, s. nigrum and m. chenopodiifolia) were then sawn on the pots. the pots were irrigated with distilled water every three days for six weeks. the seedlings were irrigated with 100 ml nutrient solution containing 2.46 g/l kh2po4 ، 4.72 g/l kno3, and 0.27 g/l ca(no3)2  every eight days instead of the distilled water. for the analysis of plant dry matter, the leaf materials were washed well with double-distilled water and dried at 70°c for 48 h. about 0.1 g of dry leaf sample was added to a 25 ml beaker and ashed in a muffle furnace for 6 h at 500°c. the ash was taken up in 10 ml 10% hno3 and the digest was finally made up to 50 ml in 10% hno3. the solutions were analyzed for elemental composition by aas. all soil samples were air-dried and sieved to