Distribution and source of contamination of heavy metal mercury at paddy field in Mandailing Natal Regency, North Sumatera, Indonesia

Abstract

Mandailing Natal Regency is administratively located in North Sumatera Province with 662,070 hectares width and a paddy field area of 40,051 hectares. Batang Gadis River stream is 180 KM long and became the source of livelihood for people in Mandailing Natal Regency as the source of drinking water, irrigation, and protein food source such as fish. Unlicensed Gold mining (PETI) occurred massively in Mandailing Natal Regency precisely at Sub-District Muara Sipongi, Sub-District Ulu Pungkut, Sub-District Huta Bargot, and Sub-District Naga Juang. The use of mercury for the amalgamation process in gold mining produces mercury waste which the run-off stream to the irrigation canals and at the end stream to Batang Gadis River Flow. This research conducted the distribution and source of contamination of heavy metal mercury at paddy fields in Mandailing Natal Regency, North Sumatera, Indonesia. The research was conducted to take soil sample analysis from paddy fields as much as 100 points from 20 paddy field locations near the amalgamation place or the water source for irrigation from Batang Gadis River that spread in five sub-districts. The soil sample analysis took for 25 cm depth. The results showed that the mercury concentration in all rice fields studied exceeded the quality standard threshold with the highest concentration found in Sub-District Naga Juang as much as 11.47 ppm followed by Sub-District Hutabargot with 10,77 ppm concentration. The factor that determines the paddy soil contamination by the mercury was the amalgamation waste which directly streams to irrigation canals compared with the paddy field with irrigation canals direct from the Batang Gadis River.