Phytoremediation Potential Of Native Plants For Co-contaminated Soils

Soil contamination is currently a critical environmental problem as it poses adverse effects to food safety and human health.Soil resources in China have faced overmuch problems and unrelenting development pressures from a longer time.Ministry of Environmental Protection and Ministry of Land and Resources of the People's Republic of China revealed the current report.According to the report Cd stands out as the most critical heavy metal for agricultural soils in China and 20%of the former industrial sites exceeds the environmental quality standards in China's in terms of inorganic and organic pollutants which mainly include pesticides,PAHs and other petroleum products.Soils contaminated with HMs and PAHs pose a risk to ecosystems because of their persistence.Accumulation of these pollutants in soil is becoming a major ecological concern because of their adverse effects on food safety and human health.Currently,remediation of soils doubly contaminated with organic and inorganic urgently requires the identification and development of economic and long-term technologies.Phytoremediation has been mostly used in single contaminants or as multiple contaminants of same type.It is a valuable technology that utilizes plants to remove and detoxify noxious or toxic pollutants from the soil.In recent times,phytoremediation has proved to be feasible and economical compared to other remediation technologies.However,effectiveness of phytoremediation varies among plant species and depends on soil and many environmental factors.For understanding the potential of phytoremediation of soils co-contaminated with different organic and inorganic pollutants,we conduct field experiment to find weather native plants species may be useful for phytoremediation of contaminated soil and to what extent.Furthermore,we individually performed greenhouse experiments in several native plants species for various aspects of phytoremediation in soils co-contaminated with organic and inorganic pollutants.Based on the above studies,we try to address issues posed by the mixture of organic and inorganic contaminants during phytoremediation of co-contaminated soils by using different indigenous plant species and to determine whether phytoremediation could be applied to co-contaminated soils.The results indicated that:(1)Native plant species have potential for varied level of metal concentration and they serve as good accumulator,indicator and excluders.However,various native wetland plant species like A.calmus,X.sibiricum and P.australis could be considered as suitable candidates for various aspects of phytoremediation and can be effective for decontamination of polluted sites as these species may serve as a good medium for phytostabilization.These species can also be used for various wetland restoration efforts.(2)Phytoremediation potential of wetland plant A.calamus on co-contaminated soil with Cd and PAHs showed that low Cd and low PAHs increased plant biomass and Cd accumulation in plant tissues,thus enhancing Cd removal.However,metals are largely accumulated in the roots,rather than the shoots,from the viewpoint of toxicology,plants that accumulate metals in their roots can be desirable as the metals would not then pass into the food chain via herbivores and thus avoid further potential risks to the environment.Dissipation of PAHs from soils was not significantly influenced by Cd addition or by the presence of plants.Correlation analysis also indicated a positive relationship between various treatments of residual concentrations of PHN and PYR(PAHs),whereas enzyme activities(DHN and PO)were negatively correlated with each other.Cluster analysis revealed similarities between different treatments during phytoremediation of Cd and PAHs.It can be concluded that A.calamus is effective for phytoremediation of soil co-contaminated with Cd and PAHs.The high biomass production and resistance to different environmental stress make them ideal candidate for uptake and removal of pollutants from contaminated soil.(3)Phytoremediation potential of herb species X.sibiricum grown in co-contaminated soil Cd and PAH showed that individual or combined contamination by Cd and PAHs had no significant differences to the control treatment except in the high Cd concentration treatment.The addition of PAHs to the soil significantly increased the concentration,accumulation,and removal of Cd.The reduction of PAH concentration in the soil with time was similar in the presence or absence of plants.At higher levels of Cd contamination,the rate of removal of pyrene decreased in both planted and non-planted soils;this effect might be due to the higher Cd content altering soil microbial activity.Analysis of soil dehydrogenase and polyphenol oxidase activities showed that soil contamination had no significant effect.It was conclude that X.sibiricum is a suitable candidate for uptake and remediation of pollutants from co-contaminated sites.(4)Phytoremediation effect of soils with mixed pollutants are widely varied with plant species with respect to root parameters and rhizosphere characteristics and the remediation potential of PAHs may vary with plant species and ecotypes.Here,we performed the greenhouse experiment to investigate the influence of the root morphology(total root length,surface area,volume and tip)on PAH uptake of two native species A.calamus and X.sibiricum as both the species have greater phytoremediation potential for contaminated areas and have extensive root system,high biomass,and have adaptability to grow well in diverse environmental conditions.Result showed that biomass of A.calamus was higher than X.sibiricum but did not show any significant different except high PAHs treatment alone.Roots of A.calamus accumulate Cd and PAHs when the concentration of contamination is low in the soil however,X.sibiricum accumulate more Cd and PAH when the concentration is high in the soils.A.calamus tended to degrade PAHs in the rhizosphere with the help of microbes that lessen the uptake of pollutants into roots and increases the biomass of the plant.However,X.sibiricum roots accumulate more Cd and PAH in the soils.Uptake of more PAHs in the plant,restrained the root structure(root tip and root expansion)and biomass that would affect the growth of X,sibiricum.Thus,X.sibiricum tended to accumulate/take up pollutants directly to reduce the amount of pollutants in the soil.Although high amount of pollutants in the plant would be toxic and harmful for X.to grow,it can still grow vigorously because of its high tolerance ability.The residual PHN concentration in the soil with time was similar in the presence or absence of plants.The analysis of Pearson's correlation demonstrates that PHN and PYR significantly correlates with specific surface area,surface area,and volume and tip number there is no significant correlation found between PHN uptake and total root length in A.calamus and X.Sibiricum.It was concluded that roots of both the plant species A.calamus as well as X.sibiricum and have potential for the remediation of co-contaminated soil.(5)Phytoremediation of soil co-contaminated with Cd and pyrene by emergent wetland plant P.australis could effectively accumulate Cd and pyrene from co-contaminated soils.The single or combined contamination of Cd and pyrene did not affect the plant growth(shoot length+shoot number)and biomass(root dry weight+shoot dry weight)relative to control except the high pyrene treatment alone.The mixture of high Cd and low pyrene lessened Cd toxicity to plants resulting in improved plant growth and increases uptake,accumulation and removal of Cd and pyrene.The dissipation of pyrene in soils was significantly influenced by interaction of Cd and pyrene and plant presence or absence.At low concentration of contaminants presence of plants enhances the removal of organic pollutants.Significant positive correlation was found between soil biological enzymes and the removal rate of pyrene in planted soil.It is concluded that the emergent wetland plant P.australis was recognized to accumulate both Cd and PYR from polluted soils.The high biomass production,root depth,the resistance to different types of toxic pollutants and environmental stress make them good candidates for uptake and removal of organic and inorganic chemicals from polluted soils.The investigation on the phytoremediation potential of co-contaminated soils by different indigenous plant species,with different organic and inorganic concentration in these studies described a rigorous assessment of this area of research.These studies could explain the ability of native plants species to remediate co-contaminated soils as well as simultaneously uptake and removes metals and dissipates PAHs from soils.From the study it was clear that phytoremediation could be applied to co-contaminated soils.