# Remediation Opportunities for Arsenic-Contaminated Gold Mine Waste
## 4 Phytoremediation
### Co-Application of Soil Amendments
#### 4.2.3. Lime and Organic Amendments  
Hydrated lime and organic amendments have been studied to assist phytoremediation projects (Table 4). A study by [PERSON] et al. [94] conducted a field experiment 10 km from the Aznalcollar mine in Spain to assess two crops of _Brassica juncea_ and soil amendments for phytoremediation. Field plots were initially fertilised with inorganic fertiliser (8:15:15 N:P:K). Seeds were planted and after the first crop, and the treatments were applied. Treatments included sugar beet lime and organic amendments including fresh cow manure and olive leaves/olive mill-waste mature compost. For the second crop, soils with a pH < 5 were lined before amendments were applied. It was identified that pH affected bioavailability and bioaccumulation over time as well as plant growth and biomass production. Organic matter improved plant survival and growth because soil conditions were enhanced. Manure treatment had the largest biomass production; however, it introduced weeds in the second crop. Compost treatment did not introduce weeds but was less effective at improving biomass and metal uptake. The soil amendments olive mill-waste compost and lime were also studied by [PERSON] et al. [93]. [PERSON] et al. [93] implemented a 2.5-year field phytostabilisation experiment using _Atriplex halimus_ and soil amendments, mature olive mill-waste compost, pig slurry, and hydrated lime. Plants assisted with organic amendments ameliorated essential soil nutrients, which improved the soil microbial community. For example, soil enzyme activities, \(\beta\)-glucosidase, urease, and arylsulphatase significantly increased when compost and pig slurry were applied compared to the control. Additionally, dehydrogenase activity and basal respiration also significantly increased for compost and pig slurry amendments compared to the controls. Overall, soil enzyme activity improved with the combination of plant and soil amendment and stimulated the soil microbial community. Phytostabilisation was achieved, ecotoxicity decreased, and water-soluble organic C increased notably with the compost and plant combination. Organic matter was lower in pig slurry, but the plant compensated for organic matter with leaf litter and plant roots. However, the lime treatment did not benefit from plant features because plants did not grow well. Organic amendments improved water-soluble N, and only compost enhanced available P. Water-soluble N was greater in lined soils, which may be a result of poor plant and microbial growth because N was mainly inorganic N and highly bioavailable. Additionally, [PERSON] et al. [93] stated that the compost and plant treatment was most effective at decreasing ecotoxicity. A similar study by [PERSON] et al. [95] also used _A. halimus_ and soil amendment compost, pig slurry, and hydrated lime for a field phytoremediation project in a semi-arid mine waste location at El Llano del Beal, Cartagena, Spain. [PERSON] et al. [95] also reported that the compost treatment had soil-ameliorating capabilities by improving organic matter, total organic carbon, and soil microbial biomass -C and -N. Plant growth was enhanced by the hydrated lime by 58%, compost by 79% and pig slurry by 89%. Organic soil amendments outperformed the hydrated lime for plant growth, which is also supported by [PERSON] et al. [93] and [PERSON] et al. [94] who reported poor plant growth in lime treatments and greater biomass production in manure treatments, respectively. Compost as a soil amendment to assist phytoremediation has proven to enhance soil conditions, organic matter, the microbial community, and plant growth and avoid the input of weeds.