Investigation of Ecological Risk (ER) and Available Ratio (AR) of some heavy metals in drill cutting of Ahvaz Oil Field in 2019

 Drill cutting is one of the largest volumes of waste generated in oil and gas exploration and production activities, which contain toxic substances, especially heavy metals, which are potentially harmful to the ecosystem. This study aimed to investigate the pollution indices, available ratio, and ecological risk of some heavy metals in the Drill cutting of the Ahvaz oil field in southwestern Iran.

30 samples of drill cutting were collected from 6 wells in 6 different depths (1250-2350 m), and there were sent to the laboratory. The total and available concentration of metals extracted by Aqua Regia method and by DTPA extracting solution and metals were analyzed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Atomic Absorption Spectrophotometry(AAS). The soil chemical and physical parameters such as organic matter, EC, and pH were also measured.

The mean total concentration (Sr, Ba, Zn, Cu, Pb, Cd) in the drill cutting samples studied 1212, 1413, 117.66, 209.83, 342.66, 2.36 mg/Kg, respectively and the available amounts of these elements 12.29, 0.50, 5.14, 14.71, 23.80 and 0.46 mg/kg were measured. The highest amount of enrichment factor 20.61 was related to Pb and the highest amount of pollution index 9.15 was related to Cd, respectively. The highest available ratio (26.40) was related to Cd. The environmental risk potential index (852.91) showed that drill cuttings have very high environmental potential risk. Also, there is a negative correlation between pH and the availability ratios of Pb, Cd, and Ba in drill cutting(p<0.05).

The average values ​​of the potential ecological risk index (RI)  of the studied elements in the drill cutting of the Ahvaz oil field were in the range of very high environmental potential risk. The results obtained from the enrichment factor(EF) and the pollution index(PI) showed that the source of contamination of the studied metals is anthropogenic activities such as oil drilling activities in the study area. Therefore, continuous monitoring of the concentration of metal contaminants in the drill cuttings as well as the use of heavy metal stabilization methods in the drilled areas is essential.