Occurrence, distribution, and potential exposure risk of organophosphate flame retardants in house dust in South Korea.

Concentrations of organophosphate flame retardants (OPFRs), which are used in various plastic products, were analyzed in house dust samples collected from three Korean cities (Suwon, n = 23; Jeonju, n = 20; Kunsan, n = 42). OPFRs, including tris (2-chloroethyl) phosphate (TCEP), tris (2-chloroisopropyl) phosphate (TCPP), and tris (1,3-dichloro-2-propyl) phosphate (TDCPP), were detected in 95%-100% of the samples analyzed, suggesting the widespread use of these compounds in Korea. The levels of TCEP, TCPP, and TDCPP in Suwon, Jeonju, and Kunsan ranged from the limit of quantitation to 46,000, 28,000, and 2400 ng/g, respectively. The concentrations of all OPFRs were significantly higher in house dust samples from Suwon than from Jeonju and Kunsan; this is likely due to the increased use of these compounds in Suwon, which may be associated with the number, volume, and variety of household products in homes. In Korean homes, the estimated daily intake (EDI) of OPFRs through house dust ingestion was lower than the guideline values; however, the EDI of OPFRs for toddlers was 30-fold greater than for adults, suggesting a limited risk to human health. This is the first comprehensive study of the occurrence and distribution of OPFRs in house dust in Korea.

Characteristics of soil organic matter (SOM) extracted using base with subsequent pH lowering and sequential pH extraction.

Humic substances from eight soils of varying properties were extracted by two different methods: (1) the traditional NaOH-extraction with subsequent acidification to different pH (approximately 1 to approximately 12) and sequential extractions using 0.01 M NaNO(3) at incremental pH (approximately 1 to approximately 11). Cumulative organic matter (OM) in the sequential extractions showed properties that were consistent with NaOH-extracted OM. The release of Al and Fe in the sequential extractions was closely related with the release of organic carbon (OC). The ratio of OC associated with humic acid (HA) and fulvic acid (FA) (the HA:FA ratio) varied widely among the soils indicating heterogeneity in their OM composition. However, a significant correlation between this HA:FA ratio and the NaOH extractable %OC content of the soils is indicative of the possible relationship between them. Between pH 5 and 7, which is a typical soil solution pH, a significant amount of HA-associated OC was soluble. In modeling metal speciation in soil solutions, it has been assumed that all dissolved organic carbon (DOC) that is active toward metal binding is associated with FA. The results of this study indicate that the validity of these assumptions based on model sensitivity alone is questionable.

The importance of organic matter distribution and extract soil:solution ratio on the desorption of heavy metals from soils.

The lability (mobility and bioavailability) of metals varies significantly with soil properties for similar total soil metal concentrations. We studied desorption of Cu, Ni and Zn, from 15 diverse, unamended soils. These studies included evaluation of the effects of soil:solution extraction ratio and the roles of soil properties on metal desorption. Dcsorption was examined for each metal by computing distribution coefficients (Kd) for each metal in each soil where Kd = [M]soil/[M]solution, Results from soil:solution ratio studies demonstrated that Kd values for the metals tended to increase with increasing soil:solution ratio. This result also held true for distribution of soil organic matter (SOM). Because the soil:solution ratio has a significant effect on measured metal distributions, we selected a high soil:solution ratio to more closely approach natural soil conditions. Copper showed strong affinity to operationally defined dissolved organic matter (DOM). In this study, DOM was operationally defined based on the total organic carbon (TOC) content in 0.45-microm or 0.22-microm filtrates of the extracts. The Kd of Cu correlated linearly (r2 = 0.91) with the Kd of organic matter (Kd-om) where the Kd-om is equal to SOM as measured by Walkley-Black wet combustion and converted to total carbon (TC) by a factor of 0.59. These values representing solid phase TC were then divided by soluble organic carbon as measured by TOC analysis (DOM). The conversion factor of 0.59 was employed in order to construct Kd-om values based on solid phase carbon and solution phase carbon. SOM plays a significant role in the fate of Cu in soil systems. Soil-solution distribution of Ni and Zn, as well as the activity of free Cu2+, were closely related to SOM, but not to DOM. Kd values for Ni, Zn and free Cu2+ in a particular soil were divided by the SOM content in the same soil. This normalization of the Kd values for Ni, Zn, and free Cu2+ to the SOM content resulted in significant improvements in the linear relationships between non-normalized Kd values and soil pH. The semi-empirical normalized regression equations can be used to predict the solubility of Ni and Zn and the activity of free Cu2+ as a function of pH.