The effect of carbon black and hair waste on heavy metals uptake and some growth parameters of lettuce and spinach irrigated with metal contaminated water

Soil quality is very important because of the direct impact on agricultural production and the nutrition of living creatures. The use of urban and industrial wastewaters (as lower quality water for irrigation of plants to reduce raw water consumption) can lead to a gradual accumulation of some heavy metals in the soil, which can enter the food chain and menace the health of creatures. Due to the high costs of the physical cleaning up methods, it is sometimes more logical to use methods that reduce the effects of contaminants in the environment. For this purpose, a pot experiment with lettuce and spinach was conducted to investigate the effect of carbon black and hair waste (as adsorbent) on the concentration of cadmium and lead in plants, as well as fresh and dry weight as affected by contaminated water irrigation. Carbon black with defined properties was prepared by the Iranian Carbon Black Company. After collecting the hair waste, all was washed with raw water, diluted acid, and distilled water properly. Then the waste was air dried and ground as much as possible to make it uniform and increase the specific area to cause more reaction between the waste and soil. The waste was applied to the soil at a rate of 3 percent by weight. The carbon black was applied to the soil at the same rate as the hair waste. After preparing the pots, spinach and lettuce were planted in the pots and irrigated with contaminated water and harvested 60 days after sowing. At the end of the pot experiment, some growth parameters, as well as the uptake of some elements, including micronutrients and heavy metals, was measured by standard methods. The data were analyzed by using SAS and graphs were plotted with the help of Excel program. So, this study was carried out in a completely randomized design with three treatments, including carbon black (two levels of zero and three percent by weight), hair waste (at two levels of zero and three percent by weight), and irrigation water (at two levels of contaminated water and Non-contaminated) with 3 replications. The results showed that the use of heavy metal contaminated water significantly reduced the growth parameters in both plants, which was significantly limited by the use of adsorbents, which shows the effect of adsorbents in reducing the negative effects of pollutants in the environment. The analysis of data showed that the effect of carbon black, hair waste, and irrigation water on fresh weight of spinach and lettuce was statistically significant (at the level of 1 and 5%). The interaction effect of carbon black and irrigation water on fresh weight of plants showed that the use of carbon black increased the fresh weight of spinach and lettuce from 16.65 to 19.68 and 11.38 to 16.68, respectively. In the case of treatment of 1.5% carbon +1.5% hair waste, the fresh weight of plants decreased significantly as compared to treatments without hair waste, as well as the control treatment. This can be due to the negative effect of hair waste on the physical properties of soil according to the short time of the research work (2 mounts). More or less, the effect of carbon black and irrigation water on iron, zinc, copper, cadmium, and lead content in both experimented plants was statistically significant. In the case of hair waste effect on iron and lead for spinach, iron and copper for lettuce were statistically significant. The irrigation with contaminated water decreased the amount of iron, zinc, and copper in the aboveground part of plants which is indicating the negative effect of heavy metals in irrigation water on root development and nutrient uptake, as well as competing through antagonistic relationships with micronutrients which are necessary for the plant growth. In the treatments containing 3% carbon black, the number of micronutrients in plants increased significantly due to surface absorption of heavy metal on carbon black and the reduction in the negative effect of heavy metals in soil. In the case of cadmium and lead, the reverse trend was observed. In spinach application of 3% carbon black decreased cadmium and lead content at the rate of 76% and 58%. In the case of hair waste, the effect on lead content at the rate of 25% was significant but for cadmium was not significant. In aboveground parts of lettuce, carbon black reduced cadmium and lead content at the rate of 69% and 54%, respectively. Same as spinach, the effect of hair waste on cadmium content was not significant. The results showed that carbon black had the highest amount of metal adsorption capacity and, therefore, can be more effective than hair waste. According to the results, carbon black can be used in the agricultural system which requires more research in the case of its ability.