RESUMO
Cigarette butts, often discarded as litter, are considered a common form of waste, containing a variety of pollutants within this hazardous residue. This study, which was designed to assess the environmental release of certain metals from cigarette butts, investigates a variety of scenarios under varying climatic conditions. Thus, in order to assess the level of metal contamination, samples of cigarette butts were collected in urban areas from seven popular brands in China, smoked artificially, and examined through graphite furnace atomic absorption (GF-AAS). The findings indicated mean concentrations of 1.77 for Cr, 2.88 for Ni, 12.93 for Cu, 24.25 for Zn, and 1.77 µg/g for Pb in the case of newly smoked butts. The emission of each of the metals increases to 8-10% when cigarette butts remain in the environment for an extended period of time. Furthermore, rainfall can accelerate metal leaching, reaching values of 18-20% compared to the controlled scenario. The worst-case scenario releases 2129.31 kg/year of metals into the environment, while the best-case scenario sees a lower release of 844.97 kg/year. The data reflect variations in metal emissions across different scenarios. There was also a strong correlation between cigarette butts in public spaces and cities. This research highlights the need to educate smokers and increase urban maintenance efficiency to reduce this litter and the metals it leaches into the environment.
RESUMO
Salvia miltiorrhiza is an important medicinal plant that experiences significant growth and biomass losses when cultivated on cadmium (Cd) contaminated soils. High Cd accumulation in plant tissues also increases the risk of metal entry into the food chain. In this study, we proposed that Cd accumulation in S. miltiorrhiza can be restricted through plant growth regulators and nutrient management. Therefore, S. miltiorrhiza seedlings were transplanted into mixed nutrient soil for two weeks, then treated with 30 mg kg-1 CdCl2, 200 mg kg-1 Na2SiO3·9H2O, and 100 mg kg-1 MnSO4, and simultaneously sprayed with 10 mg L-1 ALA on the leaves one week later. This study showed that elevated Cd accumulation significantly reduced plant growth and biomass. This growth inhibition damaged photosynthetic machinery and impaired carbon assimilation. In contrast, 5-aminolevulinic acid (ALA) significantly promoted the biomass of S. miltiorrhiza, and the dry weight of plants treated with ALA combined with manganese (Mn)/silicon (Si) increased by 42% and 55% as compared with Cd+Mn and Cd+Si treatments. Exogenously applied ALA and Si/Mn significantly activated antioxidant enzymes and promoted the growth recovery of S. miltiorrhiza. Further, exogenous ALA also reduced the Cd concentration in S. miltiorrhiza, especially when combined with Si. Compared with the Cd+Si treatment, the Cd+Si+ALA treatment reduced the Cd concentration in roots and leaves by 59% and 60%, respectively. Gene expression analysis suggested that ALA and Si significantly up-regulated genes associated with Cd transport. Other genes related to heavy metal tolerance mechanisms are also regulated to cope with heavy metal stress. These results indicated that the combined action of ALA and Si/Mn could reduce Cd-toxicity by increasing chlorophyll content and changing oxidative stress and can also affect Cd accumulation by regulating gene expression.
