Vol. 3, No. 1 (February 1997) – Preface
Environmental Monitoring Studies: The Real World
Environmental monitoring studies allow us to study the real world. However, any scientist wishing to conduct real world studies faces two enormous challenges. The first is that substances of interest in the environment are often present at extremely low concentrations – parts per billion levels are not unusual. The ability to detect one part per billion is equivalent to detecting one drop in 50,000 liters (13,000 gallons).
The second challenge is that environmental samples can be incredibly complex. For instance, treated wastewater (effluent) from a sewage treatment plant may contain 60,000 organic compounds, all present in parts per billion or lower concentrations. Consequently, the ability to detect specific compounds at extremely low concentrations is essential for documenting what happens in the environment.
This issue of The CLER Review highlights five environmental monitoring studies which have been conducted to study the environmental fate of linear alkylbenzene sulfonate (LAS) and other detergent actives (surfactants) in the real world. The first three studies focus on sewage treatment plants:
- D.C. McAvoy, WS. Eckhoff and R.A. Rapaport of the Procter & Gamble Company (Cincinnati, Ohio) report on a study of 50 sewage treatment plants in the United States and in the rivers and streams receiving treated wastewater from these plants. All of the treatment plants, except the less efficient trickling filter units, demonstrated excellent removal of LAS (96.2 to 99.3% average removals). Despite the selection of treatment plants with low effluent dilution (worst case conditions), real world levels of LAS in receiving waters were very low (typically less than 50 parts per billion) and pose little risk to aquatic and sediment organisms.
- J. Waters and T.C.J. Fei’tel of the Procter & Gamble Company (Strombeek-Bever, Belgium) report on a monitoring program conducted at five countries in Europe on the most common type of sewage treatment plant, the activated sludge unit. Very high LAS removal rates were observed (99.2% average). Consequently, LAS levels in receiving waters below treatment plant discharge points were low (9 – 140 parts per billion), well below levels that could cause any adverse effects on aquatic organisms.
- M. Trehy and colleagues from Monsanto (St. Louis, Missouri), CONDEA Vista (Austin, Texas) and Procter & Gamble (Cincinnati, Ohio) have studied LAS, DATS and their biodegradation intermediates in 10 U.S. sewage treatment plants and in the rivers and streams receiving treated effluents. The results confirm not only that LAS is efficiently removed during sewage treatment but also that LAS intermediates, DATS and DATS intermediates are significantly removed.
Two studies in this issue focus on what happens to trace levels of LAS and other detergent surfactants in rivers downstream from sewage treatment plants:
- F.R. Schroder of Henkel (Dusseldorf, Germany) reports on a study of LAS, AES, alcohol sulfate and secondary alkane sulfonate in a small river in Germany. The concentrations of the surfactants in the monitored stretches of the river below two sewage treatment plants averaged 6 parts per billion for LAS and 3 parts per billion for the other surfactants. These very low concentrations can be attributed to continuing biodegradation of surfactants in river water. In fact, high rates of biodegradation in the river were observed.
- H. Takada and colleagues at the Tokyo University of Agriculture and Technology (Japan) have also observed extremely rapid biodegradation of LAS in a shallow stream in Tokyo which receives untreated graywater (household wastewater excluding sewage). The biodegradation rate observed for LAS, a half live of only 1 hour, could not be duplicated in laboratory experiments with river water. Further investigations showed that the rapid rate of biodegradation is due to the presence of a layer of microoganisms, called “biofilm,” attached to the stream bed.
Taken together, these studies demonstrate the strength and power of environmental monitoring studies: these provide the best evidence for the environmental safety of surfactants and other detergent ingredients. This is not to say that laboratory studies are without value in predicting the real world – they do in fact have value for this very purpose as illustrated by the success of the river model in the paper by McAvoy et al., the sewage treatment models in the paper by Waters and Feijtel, and the biofilm studies in the paper by Takada et al.
Environmental modeling studies allow us to modify or confirm what we have learned in laboratory studies so that we can be assured that our conclusions reflect what happens in the real world. In short, environmental monitoring studies bring us the real world.
John E. Heinze, Ph.D.