Analysis of soil contamination by phthalate ester around tributaries to the Han river and molecular identification of the phthalate-degrading bacteria

Abstract

Phthalate esters are used as additives in plastics to improve mechanical properties, particularly flexibility. The contamination of soil samples by phthalate esters around four tributaries to the Han River was analyzed using gas chromatography/mass spectrometry (GC/MS). All soil samples collected from the four tributaries, which include Anyangcheon and Seohocheon (potential polluted areas), and Gapyeongcheon and Namhan River (potential clean areas), were found to be contaminated by bis(2-ethylhexyl) phthalate (DEHP). Soil around Anyangcheon was most highly contaminated (113 ppb), about twofold higher than the ones around Seohocheon (64 ppb), Gapyeongcheon and Namhan River (50 ppb). Based on the fact that DEHP contamination in sediments of the river tributaries around the country is as high as 2.04 ppm, it was concluded that DEHP contamination of the soils around the tributaries to the Han River is relatively low. Bacteria, using phthalates as carbon and energy sources, were isolated from soil highly contaminated with phthalate. They were then identified through 16S ribosomal DNA (rDNA) sequencing, and their substrate specificity was compared. Four different isolates were obtained from the pure culture in phthalic acid (PA)- or DEHP-containing minimal media. As a result of comparing bacterial 16S rDNA sequences with database, the isolated bacteria were found to belong to three genera: Comamonas, Acinetobacter, and Pseudomonas. Comamonas testosteroni specifically used PA as the carbon source, whereas Acinetobacter spp. and Pseudomonas tolaasii used PA and DEHP at similar frequencies. These results indicate that the phthalate metabolism depends on soil bacterial genera.