# Remediation Opportunities for Arsenic-Contaminated Gold Mine Waste
## 3 Mitigating Arsenic-Contaminated Mine Waste  
### Global Arsenic Concentrations  
Increasing arsenic concentrations are a global problem; countries such as Canada, USA, UK, Poland, Australia, New Zealand, China, Bangladesh, and India report high arsenic contaminations (Table 1) [39]. Arsenic contamination worldwide is present in soil, water, drinking water, groundwater, animals, food products, and more [39]. Arsenic background levels (uncontaminated soil) in soils worldwide have been reported to range from 0.4 to 40 mg/kg [2]. In the Canadian Northwest Territories, the Giant Mine, which was operational from 1949 to 1999, roasted Au-bearing arsenopyrite ore [21]. Poorly monitored roasting of arsenopyrite caused the release of approximately 20,000 t of As-contaminated emissions and the production of dust containing approximately 80% arsenic trioxide [21]. [PERSON] et al. [21] analysed soil outcrops and reported average As concentrations of 1550 mg/kg with a maximum of 5760 mg/kg; only 3 out of 40 samples met the Canadian soil quality guidelines for industrial soils (Table 1). [PERSON] et al. [21] also analysed soil cores (0-37 cm) and reported that surface soil (0-6 cm) presented the highest As concentrations of 7680 mg/kg, and soil at 6-15 cm depth had 323 mg/g of As. On the east coast of Canada in Nova Scotia, there were 64 mining districts that produced 34 t of gold and 3 million t of tailings during 1861-1942 [32; 52]. [PERSON] et al. [52] and [PERSON] et al. [32] reported similar As concentrations in Nova Scotia tailings, ranging from 200 to 77,000 mg/kg and 318 to 76,500 mg/kg, respectively (Table 1). The Canadian Council of Ministers of the Environment (CCME) developed the Canadian Soil Quality Guidelines for the Protection of Environment and Human Health 1997 document for inorganic arsenic. The soil quality guideline for agricultural, residential/parklands, and commercial/industrial soils are 12 mg/kg (Table 1) [53]. Mine tailings have been a problem for decades, possibly longer, and are significantly exceeding the soil quality guidelines in Canada. In England, Cornwall was a major producer of arsenic, tin, and copper during 1860-1900 and smelted imported arsenical ores [54]. [PERSON] et al. [55] conducted a pot experiment with Cornwall soils containing elevated As concentrations from mining and natural sources such as As-rich bedrock. Soil samples were collected from six sites at Camborne at a 20 cm depth then dried and sieved to <2 mm. The six sites had As concentrations of 67 \(\pm\) 2357 \(\pm\) 15,417 \(\pm\) 2361 \(\pm\) 2475 \(\pm\) 2, and 4550 \(\pm\) 52 mg/kg (Table 1) [55]. [PERSON] et al. [56] also investigated As concentrations and human health exposure in Cornwall by analysing household garden soil and dust. Arsenic concentrations in household garden soil and dust ranged from 23 to 471 and 43 to 486 mg/kg, respectively (Table 1) [56]. The Department for Environment, Food and Rural Affairs and the Environment Agency (DEFRA EA) have developed a Soil Guideline Value to limit exceedances and human exposure [57]. The soil guideline value for As is 20 mg/kg, and all As concentrations at Cornwall reported by [PERSON] et al. [55] and [PERSON] et al. [56] exceed 20 mg/kg. In Portugal, [PERSON] et al. [58] investigated As concentrations at Castromil mine because of concerns for local communities living in the city of Porto, 23 km east from Castromil mine. One hundred and six soil samples were collected at a depth of 15 cm, and As concentrations ranged from 31 to 6909 mg/kg (median: 273 mg/kg As) (Table 1) [58]. Gold mine waste with elevated As concentrations is detrimental to human and ecosystem health and has been abandoned, leaving it for future generations to restore or mitigate the toxic effects. In Southwest Poland, the Zloty Stok mine was studied by [PERSON] et al. [59]. Soil and plant material were collected and analysed for elemental concentrations to identify phytoremediation characteristics [59].