Fate of Brominated Flame Retardants and Organochlorine Pesticides in Urban Soil: Volatility and Degradation

Abstract

As the uses of polybrominated diphenyl ethers (BDEs) are being phased out in many countries, soils could become a secondary emission source to the atmosphere. It is also anticipated that the demand for alternative brominated flame retardants (BFRs) will grow, but little is known about their environmental fate in soils. In this study, the volatility and degradation of BFRs and organochlorine pesticides (OCPs) in soil was investigated. A low organic carbon (5.6%) urban soil was spiked with a suite of BFRs and OCPs, followed by incubation under laboratory condition for 360 days. These included BDE- 17, -28, -47, -99; α- and β-1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), β-1,2,5,6-tetrabromocyclooctane (TBCO), and 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE), OCPs: α-hexachlorocyclohexane (α-HCH) and (13)C(6)-α-HCH, trans-chlordane (TC), and (13)C(10)-TC. The volatility of spiked chemicals was investigated using a fugacity meter to measure the soil-air partition coefficient (K(SA)). K(SA) of some spiked BFRs and OCPs increased from Day 10 to 60 or 90 and leveled off afterward. This suggests that the volatility of BFRs and OCPs decreases over time as the chemicals become more strongly bound to the soil. Degradation of alternative BFRs (α- and β-TBECH, β-TBCO, DPTE), BDE-17, and α-HCH ((13)C-labeled and nonlabeled) was evident in soils over 360 days, but no degradation was observed for the BDE-28, -47, -99, and TC ((13)C-labeled and nonlabeled). A method to separate the enantiomers of α-TBECH and β-TBCO was developed and their degradation, along with α-HCH ((13)C-labeled and nonlabeled) was enantioselective. This is the first study which reports the enantioselective degradation of chiral BFRs in soils. Discrepancies between the enantiomer fraction (EF) of chemicals extracted from the soil by dichloromethane (DCM) and air were found. It is suggested that DCM removes both the sequestered and loosely bound fractions of chemicals in soil, whereas air accesses only the loosely bound fraction, and these two pools are subject to different degrees of enantioselective degradation. This calls for caution when interpreting EFs obtained from DCM extraction of soil with EFs in ambient air.

Environmental behavior of the enantiomers of the chiral fungicide metalaxyl in Mediterranean agricultural soils

“…Only for soil 1, the two-compartment model resulted in smaller χ 2 minimum error value (at which the test is passed at the 5% significance level) than the single first-order model for both enantiomers (Table 3) The superior fitting of metalaxyl dissipation data to the two-compartment model for the clay soil (soil 1) suggests that a fraction of the added pesticide in this soil could have displayed reduced bioavailability, thus dissipating at a relatively slower degradation rate, than the more available fraction typically present in the accessible soil solution phase (Beulke and Brown, 2001). This behavior would also explain the reduced enantioselectivity of metalaxyl degradation in soil 1, because the protected, less bioavailable fraction is expected to be more racemic than the fraction readily available to enantioselective biodegradation, since it is supposed to have undergone less microbial attack (Ulrich et al, 2009;Wong et al, 2012).…”

“…2), and the high smectite+illite content of this soil (Table S1) should have provided the soil with additional clay interlayer space upon swelling of the clay minerals in contact with water (Nagpal et al, 1972). Therefore, sorption and entrapment in the abundant small-size pores of soil 1 are likely to have reduced the availability of metalaxyl enantiomers for microbial degradation, and also to have reduced the enantioselectivity of the metalaxyl degradation process, the latter because the less bioavailable pesticide fraction is supposed to remain racemic longer than the readily biodegradable fraction (Ulrich et al, 2009;Wong et al, 2012).…”

“…Nevertheless, although the fit to the two-compartment model cannot be used as a direct evidence for entrapment, it suggests the presence of an important pesticide fraction with reduced bioavailability in the clay soil. It has recently been observed that chiral organochlorine pesticides in sequestered and bioavailable soil compartments, which were differentiated by means of chemical extraction methods, were subjected to different degrees of enantioselective degradation (Wong et al, 2012).…”

Influences of artificial root exudate components on the behaviors of BDE-28 and BDE-47 in soils: desorption, availability, and biodegradation

“…Therefore, it is important to elucidate the desorption and availability of PBDEs in soils, particularly under the influences of biological activity such as root exudation. On the other hand, PBDEs can be broken down into lower brominated congeners by soil microorganisms (Lee and He 2010;Wong et al 2012) and bring additional adverse influences to bear on the environment and human health due to their different biological effects compared with their precursor PBDEs. However, it still remains unclear whether the enhanced degradation rate of PBDEs by microbial activities is associated with the effects of root exudates and how root exudate components act on the biodegradation of PBDEs in soils.…”

Chiral Chemicals as Tracers of Atmospheric Sources and Fate Processes in a World of Changing Climate

“…movement of chemicals from exchangeable to sequestered pools. 21,62,63) b) Climate change is predicted to impact accumulation and release of POPs from the forest canopy, 64) and chiral POPs might be useful for following cycling within the forest ecosystem 21) ; e.g., volatilisation from soil, atmospheric deposition, foliar uptake and release, and metabolism within plant tissues. c) Summer ice cover is decreasing in the Arctic Ocean, as a whole 65) and in the Canadian Archipelago-Beaufort Sea, 66) and September 2012 was the lowest coverage on record.…”