ABSTRACT
Biochar shows unique advantage in decreasing the bioavailability of phenanthrene and has huge potential into the in-situ remediation of contaminated sediment. The different order spiking influences the bioavailability and ecological risk of phenanthrene, this study provides a comprehensive investigation of biochar (derived from mangrove Kandelia obovata -sediment system under three conditions: I) co-addition of biochar and sediment; II) biochar and subsequently sediment addition (after biochar adsorption reached equilibrium); III) sediment and subsequently biochar addition (after sediment adsorption reached equilibrium). It was observed that the adsorption capability under model I and III was much smaller than that under model II (p < 0.05). Regardless of time, K. obovate - biochar significantly (p < 0.05) increase the sorption of phenanthrene in sediment -water system. The results provide valuable studies for further in-situ remediation of phenanthrene and engineering applications.
ABSTRACT
Cd has high activity and bioavailability and is a poisonous element to plants. As a critical ecosysterm, mangroves are subjected to serious Cd pollution. In this research, the hypothesis was presented that improving Fe bioavailability would alleviate Cd phytotoxicity to Avicennia marina (Forsk.) Vierh. To test this, we examined the effect of four exogenous Fe and three Cd concentrations on A. marina. The results showed that a significant positive correlation excited between moderate exogenous Fe concentration and Cd tolerance of A. marina. Moderate exogenous Fe concentration directly or indirectly promoted the formation of Fe plaque, which immobilised more Cd on the root surface and decreased Cd absorption in roots. Furthermore, an exogenous Fe application increased plant biomass and Fe accumulation in A. marina tissues. This improved the competition between Fe and Cd within the plants. Therefore, an Fe application facilitated a decrease in Cd toxicity within A. marina. Simultaneously, a moderate Fe concentration caused an increase in low-molecular-weight organic acid (LMWOA) secretion from the roots. Meanwhile, Cd can be chelated/complexed by LMWOAs. It also played a crucial role in Cd detoxification in A. marina. In conclusion, Fe application accelerated the growth and enhanced Cd tolerance of A. marina. Therefore, improving Fe bioavailability will protect mangroves from Cd contamination.
Subject(s)
Avicennia/drug effects , Cadmium/toxicity , Iron/therapeutic use , Plant Roots/drug effects , Avicennia/chemistry , Iron/pharmacology , Plant Roots/chemistryABSTRACT
Avicennia marina is a high-Cd-tolerant species in the mangrove wetlands. A hydroponic experiment was carried out to research the accumulation and chemical form distribution of Cd in the tissues of A. marina under different concentrations and durations of Cd stress. It was found that the concentrations of Cd in plant tissues followed the order of root > stem > leaf. The data suggested that root activity decreased, Cd accumulation ability weakened in roots, and the translocation factor increased in stems and leaves with the increase of stress duration. With a proactive defense mechanism, most Cd was bound to pectates, organic acids, and protein, especially in roots and stems with the most proportion of 88.51 and 78.91%, respectively, having lower biological activities. The Cd bounded to water-soluble organic acid and free inorganic aminophenol-Cd showed the lowest concentration. The pectates, organic acids, and protein-integrated Cd seem the most important in affecting Cd detoxification for A. marina; this mechanism of change in Cd biological activities decreases the toxicity of this aggressive pollutant and presents new knowledge about the tolerance of mangrove plants.
