Living with a large reduction in permited loading by using a hydrograph-controlled release scheme

The Total Maximum Daily Load (TMDL) for ammonia and biochemical oxygen demand for the Pee Dee, Waccamaw, and Atlantic Intracoastal Waterway system near Myrtle Beach, South Carolina, mandated a 60-percent reduction in point-source loading. For waters with a naturally low background dissolved-oxygen concentrations, South Carolina anti-degradation rules in the water-quality regulations allows a permitted discharger a reduction of dissolved oxygen of 0.1 milligrams per liter (mg/L). This is known as the 0.1 rule. Permitted dischargers within this region of the State operate under the 0.1 rule and cannot cause a cumulative impact greater than 0.1 mg/L on dissolved-oxygen concentrations. For municipal water-reclamation facilities to serve the rapidly growing resort and retirement community near Myrtle Beach, a variable loading scheme was developed to allow dischargers to utilize increased assimilative capacity during higher streamflow conditions while still meeting the requirements of a recently established TMDL.As part of the TMDL development, an extensive real-time data-collection network was established in the lower Waccamaw and Pee Dee River watershed where continuous measurements of streamflow, water level, dissolved oxygen, temperature, and specific conductance are collected. In addition, the dynamic BRANCH/BLTM models were calibrated and validated to simulate the water quality and tidal dynamics of the system. The assimilative capacities for various streamflows were also analyzed.The variable-loading scheme established total loadings for three streamflow levels. Model simulations show the results from the additional loading to be less than a 0.1mg/L reduction in dissolved oxygen. As part of the loading scheme, the real-time network was redesigned to monitor streamflow entering the study area and water-quality conditions in the location of dissolved-oxygen sags. The study reveals how one group of permit holders used a variable-loading scheme to implement restrictive permit limits without experiencing prohibitive capital expenditures or initiating a lengthy appeals process.     

Multiresidue analysis of organophosphate and pyrethroid pesticides in duplicate-diet solid food by pressurized liquid extraction

An analytical method was developed for determining organophosphate pesticides (OPP) and pyrethroid pesticides (PYR) in duplicate-diet solid food. The method consisted of pressurized liquid extraction (PLE) with dichloromethane followed by cleanup with gel permeation and solid phase extraction columns and gas chromatography/mass spectrometry (GC/MS) analysis. Quantitative recoveries (73–117 %) of the target pesticides were obtained for spiked duplicate-diet food samples. The percent standard deviation (% RSD) of replicate food samples was within ± 20 %. Another method was developed for determining a common OPP metabolite, 3, 5, 6-trichloro-2-pyridinol (TCP) in duplicate-diet food. The method consisted of a PLE with methanol followed by liquid-liquid partitioning, derivatization, and GC/MS analysis. Recoveries of TCP ranged from 83 to 101 % for spiked duplicate-diet food samples. The % RSD of replicate food samples was within ± 15 %. The results confirmed that these methods are reliable and robust, and that they can be used in routine analysis. In addition, a storage stability study for a common OPP, chlorpyrifos (CPF), in solid food samples was performed. The fortified ¹⁵N-¹³C-labeled CPF was stable over 16 mo storage at ?20° C in the dark. The developed analytical methods were successfully applied to 278 duplicate-diet food samples from preschool children, demonstrating that these methods are robust and suitable for routine analysis in future exposure monitoring studies.     

Sorption of carbamazepine, 17α-ethinylestradiol, iopromide and trimethoprim to biomass involves interactions with exocellular polymeric substances

The sorption of carbamazepine (CBZ), iopromide (IOP), trimethoprim (TMP) and 17α-ethinylestradiol (EE2) was evaluated using four biomass types (pure ammonia oxidizing bacterial culture, two heterotrophic enrichment cultures with varying levels of oxygenase activity, and a full-scale nitrifying activated sludge (NAS) culture). CBZ and IOP did not sorb to the four biomass types. EE2 did not sorb to the pure culture but sorbed significantly to the heterotrophic cultures and NAS. TMP sorbed to the heterotrophic cultures and NAS, and was not evaluated for the pure culture. Three floc characteristics (hydrophobicity, median particle size, organic matter content) correlated moderately well with the EE2 organic matter sorption coefficient (K_OM,EE2). Zeta potential did not correlate well with K_OM,EE2 but did with K_OM,TMP, indicating that TMP sorption is more influenced by electrostatic factors than EE2. Once divalent cation-linked exocellular polymeric substances (EPS) were removed from flocs, EE2 and TMP sorption to the non-EPS (cellular) fraction decreased by approximately 50%. The correlation between K_OM,EE2 for the non-EPS cellular fraction deteriorated while the correlation between K_OM,TMP improved. EE2 seemed to sorb more strongly to EPS protein whereas TMP sorbed equally to polysaccharide and protein EPS. Attempts to develop predictive models were not successful. Pharmaceuticals that sorbed to biomass samples underwent biodegradation whereas those that did not sorb were not biodegraded, suggesting a relationship between sorption and pharmaceutical biotransformation.