A Novel Approach to Field Monitoring for Use in Risk Assessment: A Case Study on Organohalogen Formation from Domestic Hypochlorite Bleach, Involving Participation of a Small Community. F. Racioppi, Procter & Gamble, Rome Technical Center, Italy; D. Schowanek, E. Matthijs, and R. Boyko, Procter & Gamble - European Technical Center, Strombeek-Bever, Belgium; M. Gabba, and A.Buschini, Biotecnologika, Felino, Italy; and G. P. Gardini, Department of Organic and Industrial Chemistry, University of Parma, Parma, Italy
SUMMARY
A novel field monitoring approach, involving the active participation of the inhabitants of a small community in the Italian town of Panna, was used to assess the effect of the use of household hypochlorite bleach on the formation of organohalogens (AOX) in domestic sewage under realistic usage conditions. The study showed a very good correspondence between predicted and measured AOX concentration and hypochlorite-to-AOX conversion rate in domestic sewage. The concept of this field study is considered to be re-applicable to other studies on consumer chemicals, and can confer additional confidence to environmental exposure assessments of chemicals used in household products.
INTRODUCTION
Sodium hypochlorite (NaOCl) bleach is a household product commonly used especially in Southern Europe (e.g. Spain, France, Italy). It is used for toilet bowl and hard surface cleaning, laundry bleaching and disinfection (FIFE, 1993). Sodium hypochlorite is a highly reactive chemical, which is rapidly converted during and after use to a diversity of reaction products, with oxidation of organic and inorganic compounds being the predominant reaction mechanism. This yields to various oxidation products and chloride ions (Consultative Expert Group Detergents-Environment, 1989). Halogenated organics may also be produced at trace concentrations by addition and substitution reactions (Jolley, 1975).
An aspect which until recently was not deeply investigated is the organohalogen formation by domestic use of bleach. Data coming from laboratory simulations situate the degree of NaOCl-to-AOX conversion (% w/w) between 0.1% to 6% for the various domestic applications (Jolley, 1975; Office of Nature Conservancy Sweden, 1992; FIFE, 1993; Smith, 1994).
Starting from these premises, it was considered that a field study was useful in verifying whether the estimes of AOX formation from domestic use of bleach, as reported in the literature, could be confirmed under realistic conditions.
STUDY DESIGN
Schematically, the study consisted of three phases, each one lasting three weeks: 1. an "undisturbed period," to record baseline values on AOX concentration in domestic sewage (referred to in the study as phase IIA); 2. a "no bleach period" during which the site inhabitants were requested to stop any use of hypochlorite bleach (phase IIB); and 3. a "controlled bleach usage period," during which the inhabitants were provided with a bleach of known hypochlorite concentration to measure the degree of hypochlorite-to-AOX conversion (phase IIC). Before the conduction of the study, a "pilot phase" lasting one week was carried out to characterize the experimental site, and to identify and solve any relevant logistic/experimental issue.
CHARACTERISTICS OF THE EXPERIMENTAL SITE
The site selected for the study was located in a newly built area in the Italian town of Parma. It consisted of five blocks, for a total of 155 apartments, housing ca. 420 inhabitants. The site lies at the beginning of the municipal sewage network, thus excluding any uncontrolled upstream input. It is served by separate sewer systems for domestic sewage and rain water. The buildings are served by tap water coming from two wells, treated with chloride dioxide and hypochlorite respectively. The waters coming from the two wells merge before being distributed to the study site.
INVOLVEMENT OF THE SITE INHABITANTS
The representativeness of the study site in terms of bleach consumption habits for Italy was assessed before initiating the experimental part. A market research agency gathered information about the presence of bleach users and their bleach consumption patterns via telephone interviews. Results were judged as acceptably in line with the known Italian consumer habits.
In the second phase of the main experiment (referred to as phase BB), the inhabitants were asked to completely stop the use of bleach for three weeks. No alternatives were suggested. Detailed instructions were provided by various means, including posters, personal letters and pre- and post awareness interviews. To reinforce the importance of stopping bleach usage, the site inhabitants were asked to hand in their bleach bottles for the entire duration of phase IIB, Before starting phase IIB the awareness of the study was found to be high (89%), and finally 99% of the inhabitants claimed to have adhered to the instructions.
In the third phase (referred to as phase IIC), the site inhabitants were supplied with bleach of known composition in replacement of their own bleach bottles. The total consumption of bleach was measured by weighing the bottles before and after the study phase.
EXPERIMENTAL ASPECTS
Flow -proportional composite samples were
obtained by means of a bubbler flowmeter connected to an
automatic sampler.
For the study, a mixture of stratification
and composite sampling procedures under a random sampling
regime was selected. The periods of the main study phases
lasted three weeks. Each day was stratified into three
eight hour periods (dayparts) : 0:00-08:00, 08:00-16:00
and 16:00-24:00.
Absorbable Organic Halogens : The
international standard ISO 9562 (1989) "Water
Quality : Determination of absorbable organic halogens
(AOX)" was used m this field study. AOX (X = Cl
+ Br + I) was selected because it is probably the most
adequate, broadly accepted and practical estimator of the
total amount of organohalogens present in aqueous
samples. As for tap water, the AOX level was found to be
virtually constant over the study period, with an average
of ca. 15 µg AOX.1-1.
Non-AOX parameters : FAC, TAC, pH
Temperature and DO measurements were made on grab
samples. Conductivity, chloride, BOD, COD, nitrogen
parameters and suspended solids were determined on
flow-proportional composite samples. Over the study
period, the analysis indicated a sewage composition
within normal range.
Flow measurements : The flow was recorded continuously by mean of the flowmeter. These measurements were cross-checked with readings of the water meters in the buildings resulting in a daily consumption of about 62 m3 (147 1.inhabitant-1 .day-1). The average relative contribution of the different dayparts to the total flow was as follows : 27% (0:00-8:00 h), 38% (8:00-16:00 h) and 35% (16:00-24:00 h).
RESULTS
Effect of sodium hypochlorite on the AOX level of
domestic sewage
Results can be summarized as follows:
The above observations suggest an effect of bleach usage on
the average AOX levels, with the majority of the AOX being formed
during the day. When taken together, these daypart differences
translate into statistically significant differences (
= 5%) between Phase IIB
and the two bleach use phases. The latter were not significantly
different. In the no-bleach period (IIB) the mean AOX value is
106 µg.1-1, versus 143 µg.1-1 in the
"undisturbed bleach use period" (IIA). Hence the
difference in AOX level is about 37 µg.1-1. The fact
that in phase IIC the AOX level (158 µg.1-1) returned
to a level comparable to that in phase IIA, can be seen as an
internal control for the experiment.
The emission of AOX, expressed as a total daily AOX emission
per inhabitant, was around 22 mg. Of this amount, 7.0 - 7.5 mg
can be attributed to the use of domestic bleach. The contribution
of bleach to the total AOX emission is therefore in the range of
30 - 35% at this particular site.
Determination of the NaOCl to AOX conversion efficiency
The degree of NaOCl-to-AOX conversion (% w/w) was calculated as the ratio of the net AOX formed (g AOX per 21 days) over the weight of NaOCl used over the IIC experimental period (g NaOCl per 21 days). The bleach contained 4.73% NaOCl. The volume of commercial bleach used was of the order of 83 kg per 21 days (= 76 l), which corresponds to ca. 3950 g NaOCl. The AOX background in the bleach was ca. 12 mg.l-1.
The net AOX emission can be calculated as the AOX emission in Phase IIC, from which the AOX emission in phase IIB and the AOX background in bleach are subtracted: 194 - 131 - 1 = 62 g per 21 days. Hence, the NaOCl-to-AOX conversion efficiency was of the order of 62 g/3950 g = ~ 1.5%.
DISCUSSION
AOX formation from domestic bleach : comparison of
laboratory and field data
Field studies are important tools to validate results obtained in the laboratory or via theoretical calculations. It was in this context that the AOX monitoring program was executed.
Laboratory studies by other research groups on the degree of halogenation of organic compounds by hypochlorite during domestic tasks, or during effluent disinfection, reveal a relatively consistent picture, with values ranging roughly between 0.1% (Consultative Expert Group Detergents-Environment, 1989) to a maximum of ca. 6% for some applications (FIFE, 1993). The average value is to be situated around 1%. In our field study, the degree of NaOCl-to-AOX conversion was on average 1.5%, with 0.54 and 2.6 as 95% confidence limits. Hence, the correlation between field and laboratory data is excellent, and confers additional precision to the estimates of AOX formation from domestic bleach.
The average AOX concentrations observed in this study fall within the typical range for domestic sewage across Europe (50 - 250 µg.1-1; FIFE, 1993). In absolute terms, the difference in sewage concentration between a "no bleach" and an "undisturbed" bleach use situation was in the order of 37 µg AOX.1-1. Hence, hypochlorite bleach contributed ca. 30% of the total AOX. It should be considered, however, that these values are only representative for our particular study site, and may vary significantly according to the local situation. At the Parma site tap water contributed 10 - 15% (15 µg AOX.1-1). Other sources of AOX, which were not quantified individually, accounted in total for more than 50 % of the AOX at the site. These may comprise, for example, bleached toilet paper, laundry-, automatic dishwashing-, and various cleaning products, preservatives and antibiotics, food and human metabolism, as well as traces of natural AOX Hagendorf, 1992; Haas, 1994).
CONCLUSIONS
A novel field monitoring approach, which involved the
voluntary participation of the inhabitants of a small community,
was used to assess the effect of the use of a household product
on the composition of domestic sewage. The choice of the method
was driven by the desire for a high degree of realism. The
excellent agreement between the study results and data published
in the literature or generated by Industry (FIFE, 1993), mostly
under laboratory conditions, confirm the reliability of
calculation models in predicting with a reasonable degree of
accuracy the environmental concentrations of AOX resulting from
household use of hypochlorite bleach. We expect the concept of
the method to be applicable to other exposure assessment studies
on consumer chemicals which are susceptible to undergo rapid
(bio)degradation.
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