###### Abstract  
The development of phytoremediation technology is constrained by gentle phytoextraction efficiency and slow biomass accumulation. In this study, a combined remediation of pioneer plants and solid waste towards Cd- and As-contaminated farmland soil was explored. Pioneer plants _Cymodon dactylion_ and two material formulas (Steel slag (SS):pyrolusite (PY):ferrous sulfide (FS) = 3:3:2 or 1:2:8) were used in pot experiments. The DTTPA method was used to extract the bioavailable heavy metals from soil, and then, the reduction rates of the bioavailable heavy metals were calculated. After harvesting plants, data of moisture content, biomass, root length and plant height were obtained. The remediation effect was evaluated according to the above indexes. The experimental results showed that the remediation effect of _Bidentis pilosa_ was better than that of _Cymodon dactylion_. The addition of solid waste material significantly reduced the content of bioavailable Cd and As in soil by 97.73% and 53.54%, respectively. Suitable wastes may be a potential addition to heavy metal contaminated soils to promote phytoremediation of heavy metals.  
contaminated soils; heavy metal; native pioneer plants; phytoremediation; solid waste material Article Combined Remediation Effects of Pioneer Plants and Solid Waste towards Cd- and As-Contaminated Farmland Soil  
[PERSON], [PERSON], [PERSON], [PERSON], [PERSON], J. Combined Remediation Effects of Pioneer Plants and Solid Waste towards Cd- and As-Contaminated Farmland Soil
Up until now, there is an acute need for phytoextraction assisted combined remediation technology with excellent efficiency, safety and controllability [8].  
It has been recognized that heavy metal ions could be released and mobilized from contaminated soil under the facilitation of hyperaccumulators in the root-soil interface (defined as rhizosphere) [9; 10]. Particularly, in the assistance of the phytoextraction process, for the soil contaminated by Cd and As, the mobile Cd and As fractions in the rhizosphere were much greater than those in bulk soils [11; 12]. In this case, if solidifying material was involved, it could be reasonably hypothesized that the content of Cd and As of bioavailable state in soil could be reduced dramatically by using phytoextraction remediation technology assisted by materials [13; 14; 15]. In addition, solidified materials can promote the secretion of organic acids by plant roots, which can transform heavy metals in soil into bioavailable heavy metals and then be absorbed and utilized by plants. Some attempts have been made. [PERSON] et al. [16] added hydroxyapatite and giant fungus to repair the farmland polluted by Cu and Cd, reducing the content of effective copper by 72.43% and the content of effective cadmium by 48.24%. [PERSON] et al. [17] studied the remediation effect of Cd in wheat weakly alkaline soil using zeolite, diatomaceous earth and sodium-based bentonite as the main remediation components, supplemented by calcium dihydrogen phosphate and fulvic acid. Field experiments showed that Cd concentrations in rhizosphere and non-rhizosphere soils decreased by 27.3-31.2% and 34.3-54.2%, respectively.  
In our preliminary study, a formula for solidifying material (Steel slag:pyrolusite: FeSO\({}_{4}\) = 1:2:8) was especially efficient for the reduction in the bioavailable state of Cd and As. Therefore, if pioneer plants were first selected in contaminated sites and then combined with this formula for remediation, the content of bioavailable heavy metals in contaminated soil could be reduced. In this study, the soil in the affected area of an arsenic smelting slag factory in Zhongshan, Guangxi, China, was combined and remediated by pioneer plants and solid waste materials.  
The objectives of this study are the following:  
1. To study the soil pollution in the contaminated area.
2. To study the combined remediation effect of potential plants and solid waste material.