Results
3.1. Air measurements
Endotoxin concentrations in air were measured at 31 locations,
described in Table 1, yielding 79 air samples. Of these
samples, 6 samples were excluded due to failure of equipment,
34 samples (taken at 19 locations) exhibited endotoxin
concentrations above the detection limit of 0.8 EU/m3 and the
other 39 samples exhibited endotoxin concentrations below
this detection limit.
The average distance between the fountain and the air
measurement equipment was 8 m (GM, range 0.5e49 m) with
18 measurements performed within a distance of 2 m, 16
measurements performed at a distance between 2 and 10 m
and 39 measurements performed at a distance greater than
10 m. According to the Royal Netherlands Meteorological
Institute, all measurements took place at a wind speed below
three Beaufort (5.5 m/s). Furthermore, all measurements took
place on dry, cloudy days with temperatures below 20 C.
Thirty measurements (41%) were carried out at locations
where the water spray was tangible by the sample taker during
installation of the measuring equipment. Twenty-two
measurements (30%) were performed downwind, and during
the other 51 measurements (70%) no main wind direction was
observed. Forty-five measurements (62%) were executed at
locations that were sheltered from wind; during the other 28
measurements (38%), the fountain was influenced by the wind
causing aerosols to be entrained in a certain direction.
The concentrations of endotoxin in air ranged up to
85.5 EU/m3, the average concentration (GM) was 10 EU/m3
(Table 1). Statistical analysis showed that there were no differences
between concentrations of endotoxin in air and type
of fountain, such as fountains in a pond or a canal, ornamental
features or interactive features (T-test: p > 0.2). The
concentration of endotoxin in air at water features was
dependent on the water source from which water features
were filled. The concentration of endotoxin in air at sites fed
by surface water contaminated by a combined sewer overflow
(CSO) was significantly higher than locations which received
surface water or tap water as its source water (T-test: p < 0.05).
No statistical significant difference was found between the
concentrations of endotoxin in air measured at water features
fed by surface water as compared with tap water