August 2014
Untreated wastewater discharge is a common occurrence in many parts of the world, and yet there is very little data to form an environmental risk assessment. Conducting widespread monitoring studies of these types of locations on a global basis would be a tremendously ambitious and costly undertaking. Fortunately, two studies focused on developing a risk assessment for untreated wastewater discharged to the Balatuin River in The Philippines have been carried out and reported in two publications.
The first paper, by Dyer et al., focuses on the influence of physical and chemical factors — including levels of LAS — on aquatic communities in the river, including algae, invertebrates, and fish.1 The study included nine sampling sites (6 along the Balatuin River and three point sources) spread over approximately 10 miles. The sample sites ranged from residential areas that had piggeries and included direct discharge household wastes from bathing, washing of clothes including use of laundry products containing LAS, household cleaning, human wastes (urine and feces) and other solids and plastics as well. Key points that emerged from the study of the Balatuin River are:
• The study found that the critical factors impacting aquatic communities were low dissolved oxygen (DO) levels and high ammonia concentrations.
• Perhaps not surprising was the observation that river water quality was poorer at sampling points located in highly populated areas, likely due to higher waste loading at these sites.
• Sampling sites down river from those with the poorer water quality exhibited higher levels of dissolved oxygen and hence improved water quality, due in part to the purification process of the river itself.
• An initial risk assessment may be conducted for LAS concentrations in down-river sampling sites. The first step was to determine a Predicted No Effect Concentration (PNEC) for aquatic organisms. For LAS there is an extensive database and the PNEC for the most sensitive 5% of the aquatic population (PNEC0.05) – in other words, a PNEC that protects 95% of the aquatic population – can be determined. The PNEC0.05 for LAS with an average alkyl carbon chain length of C12 (C12-LAS) was determined to be 245 micrograms LAS per liter (245 μg/L) or (0.245 milligrams/L (0.245 mg/L).
• The concentration of LAS measured at six sampling sites on the Balatuin River ranged from 0.003 mg/L to 0.12 mg/L.
• Measured LAS concentrations in the Balatuin River are below the PNEC0.05 indicating no adverse effect from the presence of LAS in the river water at any of the six sampling sites.
The second study, by McAvoy et al., reports the results of a risk assessment model developed for untreated wastewater discharge containing consumer product ingredients.2 The model involves an impact zone concept in which the river can be thought of as a natural wastewater treatment system. After the river has recovered via “self-purification” (biodegradation of bulk organic compounds (BOD), conversion of ammonia to other compounds, etc.), it can be assessed by traditional risk assessment methods, focusing on DO and ammonia concentrations as critical parameters. This model (the QUAL2E model3) was validated using data obtained from the same river discussed above (the Balatiun River located in the Philippines near the same sampling sites as discussed in the Dyer paper). Sampling sites ranged over an approximately seven miles stretch of the river.
• A key takeaway is that the data show that LAS biodegrades faster than BOD, the biodegradation of which is a key driver of low DO levels. Consequently, LAS concentrations are not critical factors which influence the risk assessment. LAS is certainly present in untreated wastewater. But this risk assessment shows that standard water quality parameters — DO, ammonia, and BOD — are in fact the critical factors for an aquatic risk assessment.
• The model simulation did an excellent job of predicting the observed LAS river water concentrations. This rate loss rate of LAS is very similar to a field derived loss rate determined by Fox et al.4 and a laboratory derived value by Peng et al.5 further supporting its use. A maximum LAS concentration of 150 μg/L was predicted below a direct discharge site and by the time that parcel of water had reached the last sampling site in the study the LAS concentration was predicted to be 3 μg/L. This change accounts for a 98% loss of LAS over a 14 kilometer stretch of river and is similar to the removal in activated sludge wastewater treatment (McAvoy et al.,6).
• The 2- and 3-phenyl position isomers were being lost at a much greater rate than the inner 5- and 6-phenyl isomers within the impact zone. This shift in isomer distribution is similar to what is observed during activated sludge wastewater treatment where the primary removal mechanism of LAS is by biodegradation.7,8 The similarity in the shift in the positional isomers is further evidence that the observed LAS removal in river water is due to biodegradation.
• To determine the concentration of LAS that would interfere with the self-purification process, the key processes involved need to be identified. These are digestion of BOD (ultimately leading to increasing DO) and nitrification of ammonia. Bressan et al.9 reported a no observed effect concentration (NOEC) for LAS of greater than 200 mg/L for activated sludge (BOD) digestion and a NOEC of greater than 100 mg/L for nitrifying bacteria. Consequently, a conservative estimate of the self- purification PNEC for LAS is 100 mg/L.
• Based on the model simulation, the highest predicted LAS concentration in the impact zone was 150 μg/L. Using this value for the impact zone Predicted Environmental Concentration (PEC) and the PNEC of 100 mg/L yields a risk quotient (PEC/PNEC) of 0.0015, which indicates low risk and no cause of concern.
KEY REFERENCES
1. Dyer, S.D., C. Peng, D.C. McAvoy, N.J. Fendinger, P. Masscheleyn, L.V. Castillo and J.M.U. Lim, “The Influence of Untreated Wastewater to Aquatic Communities in the Balatuin River, The Philippines.” Chemosphere 52, 43-53 (2003).
2. McAvoy, D.C., P. Masscheleyn, C. Peng, S.W. Morrall, A.B. Casilla, J.M.U. Lim and E.G. Gregorio, “Risk Assessment Approach for Untreated Wastewater Using the QUAL2E Water Quality Model.” Chemosphere 52, 55-66 (2003).
3. Brown, L.C. and T.O. Barnwell. “The Enhanced Stream Water Quality Models QUAL2E and QUAL2E-UNCAS: Documentation and User Manual.” U.S. Environmental Protection Agency, Report No. EPA/600/3–87/007 (1987).
4. Fox, K., M. Holt, M. Daniel, H. Buckland and I. Guymer. “Removal of Linear Alkylbenzene Sulfonate from a Small Yorkshire Stream: Contribution to GREAT-ER project #7c”. The Science of the Total Environment 251/252, 265–275 (2000).
5. Peng, C.G., T. Arakaki, K.H. Jung and E. Namkung, E.. “Biodegradation of Household Chemicals in River Water Under Untreated Discharge Conditions”. In: Proceedings of IAWQ Ecohazard Specialty Conference, Otsu City, Japan (1999).
6. McAvoy, D.C., W.S. Eckhoff and R.A. Rapaport “Fate of Linear Alkylbenzene Sulfonate in the Environment”. Environmental Toxicology and Chemistry 12, 977–987 (1993).
7. Di Corcia, A., L. Capuani, F. Casassa, A. Marcomini and R. Samperi. “Fate of Linear Alkylbenzenesulfonates, Coproducts, and their Metabolites in Sewage Treatment Plants and in Receiving River Waters.” Environmental Science and Technology 33 (22), 4119–4125 (1999).
8. Morrall, S.W., W.M. Begley, J.M. Rawlings, W.S. Eckhoff and D.J. Versteeg. “Use of Isomer Distributions to Characterize the Environmental Fate of LAS.” In: Proceedings of the CESIO 5th World Surfactant Congress, May 29–June 2, Firenze, Italy, pp. 1468–474 (2000).
9. Bressan, M., R. Brunetti, S. Casellato, G.C. Fava. P. Giro, M. Marin, P. Negrisolo, L. Tallandi, S. Thomann, L. Tosoni, and M. Turchetto. “Effects of linear alkylbenzene sulfonate (LAS) on benthic organisms. Tenside Surfactant Detergents 26 (2), 148-158 (1989)
Last updated in August 2014