Iron Oxides Minimize Arsenic Mobility in Soil Material Saturated with Saline Wastewater.

The soil material in constructed wetlands is effective in retaining Se from flue-gas desulfurization (FGD) wastewater (WW), but reducing conditions can enhance native-soil As mobility. A laboratory-based soil column experiment was performed to assess the effectiveness of ferrihydrite (Fh) in minimizing the mobility of native-soil As in water-saturated soil material. A saline FGD WW mixture (i.e., influent) was delivered to columns of untreated and Fh-treated soil for 60 d. One untreated column and one Fh-treated column were then subjected to drying, followed by an additional 30 d of influent delivery. Although the influent was low in As (∼1 µg L) and the soil As level was normal, the total dissolved As concentration of effluent from the untreated columns increased with time, from ∼1 µg L to a maximum of ∼27 µg L. In contrast, effluent from the Fh-treated columns remained low in As (i.e., <5 µg L). The strong correlation between total dissolved Fe and As in the effluent suggested that reductive dissolution of native-soil Fe minerals was responsible for releasing As into solution. Results from X-ray absorption spectroscopy showed newly precipitated Fe minerals in the Fh-treated soil, and the remaining As was mainly As(V) species in both the untreated and Fh-treated soils. Thus, native-soil As mobilized under saturated conditions can be sequestered by adding poorly crystalline Fe oxides to soil prior to saturation. Furthermore, results obtained by drying and rewetting the columns showed that saturated conditions must be maintained to minimize the remobilization of sequestered As and retained Se.

Transport and Transformation of Selenium and Other Constituents of Flue-Gas Desulfurization Wastewater in Water-Saturated Soil Materials.

Constructed wetland treatment systems are used to remove selenium (Se) from flue-gas desulfurization (FGD) wastewater (WW). However, direct confirmation of the mechanism responsible for FGD WW Se retention in soil is lacking. A laboratory-based soil column study was performed to develop an evidence-based mechanism of Se retention and to study the behavior and the retention capacity of FGD WW constituents in water-saturated soil. A deoxygenated 1:1 mixture of FGD WW and raw water was delivered to the columns bottom-up at a flux of 1.68 cm d for 100 d. Some of the columns were flushed with the raw water at the same rate for an additional 100 d. Column effluent was analyzed for constituents of concern. Results showed a complete retention of FGD WW Se in the soil materials. Boron and fluorine were partially retained; however, sulfur, sodium, and chlorine retention was poor, agreeing with field observations. The FGD WW Se was retained in soil near the inlet end of the columns, indicating its limited mobility under reduced conditions. Sequential extraction procedure revealed that retained Se was mainly sequestered as stable/residual forms. Bulk- and micro-X-ray absorption near-edge structure spectroscopy confirmed that Se was mainly retained as reduced/stable species [Se(IV), organic Se, and Se(0)]. This study provides direct evidence for FGD WW Se retention in water-saturated soil via the transformation of oxidized Se into reduced/stable forms.

A soil column study to evaluate treatment of trace elements from saline industrial wastewater.

Industrial wastewater from the flue gas desulfurization (FGD) process is characterized by the presence of trace elements of concern, such as selenium (Se) and boron (B) and relatively high salinity. To simulate treatment that FGD wastewater undergoes during transport through soils in subsurface treatment systems, a column study (140-d duration) was conducted with native Kansas soil and saline FGD wastewater, containing high Se and B concentrations (170 µg/L Se and 5.3 mg/L B) and negligible arsenic (As) concentration (∼1.2 µg/L As). Se, B, and As, and dissolved organic carbon concentrations and organic matter spectroscopic properties were measured in the influent and outflow. Influent Se concentrations were reduced by only ∼half in all treatments, and results suggest that Se sorption was inhibited by high salinity of the FGD wastewater. By contrast, relative concentrations (C/Co) of B in the outflow were typically <10%, suggesting that B sequestration may have been enhanced by higher salinity. Unexpected elevated As concentrations in the outflow (at >150 µg/L in the treatment with labile organic carbon addition) suggest that soils not previously known to be geogenic arsenic sources have the potential to release As to groundwater in the presence of high salinity wastewater and under reducing conditions.

Stability of blood lead levels in children with low-level lead absorption.

Current child blood lead (Pb) screening guidelines assume that blood lead levels (BLLs) are relatively stable over time, and that only youngest children are vulnerable to the damaging effects of lower-range BLLs. This study aimed to test the stability of lower-range (≤ 10 µg/dL) child BLLs over time, and whether lower-range BLLs diminished with age among children aged 6 months to 16 years living in a lower-income neighborhood with a density of pre-1986 housing and legacy contamination. Age, sex, family income, age of residence, and/or residence proximity to point sources of Pb, were tested as potential additional factors. Capillary blood samples from 193 children were analyzed by inductively coupled plasma mass spectrometry (ICPMS). Multiple imputation was used to simulate missing data for 3 blood tests for each child. Integrated Growth Curve models with Test Wave as a random effect were used to test BLL variability over time. Among N = 193 children tested, at Time 1 testing, 8.7% had the BLLs ≥ 5 µg/dL (CDC "elevated" BLL reference value at the time of data collection) and 16.8% had BLLs ≥ 3.5 µg/dL (2021 CDC "elevated" BLL reference value). Modeling with time as a random effect showed that the variability of BLLs were attributable to changes within children. Moreover, time was not a significant predictor of child BLLs over 18 months. A sex by age interaction suggested that BLLs diminished with age only among males. Of the additional environmental factors tested, only proximity to a major source of industrial or vehicle exhaust pollution predicted child BLL variability, and was associated with a small, but significant BLL increase (0.22 µg/dL). These findings suggest that one or two BLL tests for only infants or toddlers are insufficient for identifying children with Pb poisoning.