Analisis Faktor-Faktor Yang Mempengaruhi Kadar Merkuri Rambut Pekerja Tambang Emas Tradisional Di Kecamatan Huta Bargot, Mandailing Natal, Sumatera Utara Tahun 2019 = Analysis of Factors Influence Mercury Levels of Traditional Gold Mine Workers Hair in Huta Bargot District, Mandailing Natal, North Sumatra in 2019