simple device with a big impact
A three-year EU-funded project aimed at improving
the measurement of water pollution has developed and tested equipment
for passive water sampling over a period of time, a method which eliminates
the variation often seen with the widely-used spot sampling method. Partners,
including a number of organisations from the UK, the Netherlands and Sweden,
say the new method also saves money, as repeated sampling is not needed.
It can detect inorganic or organic pollutants, and can be adapted to measure
an almost infinite range of compounds in very low concentrations.
Citizens of Europe are increasingly concerned about
the quality of their water for drinking and bathing, and want to know
that their rivers, lakes, ground water and beaches are adequately protected
from pollution from a myriad of sources. The European Union has a number
of laws in place, including the recent water policy framework directive
, which aims to monitor and limit water pollution. However, to reduce
levels of pollution they first have to be measured, and currently available
methods leave a lot to be desired.
||A point in time
Measurements of water pollutants made by spot
sampling have a major disadvantage - they assess pollution at a
single moment and can easily miss transient higher levels, e.g.
shortly after a farmer had sprayed nearby fields, or lower levels,
e.g. after heavy rainfall. "It's quite worrying," says project leader
Richard Greenwood of the University of Portsmouth, "A lot of national
government data, e.g. levels of pollutants moving down rivers, are
based on only a few spot samples per year." The new passive sampling
system will enable much more meaningful measurements to be taken
and time-averaged over a period - between two days and three weeks.
The passive sampler is a very simple device
containing a solid chromatographic receiving phase, which accumulates
the pollutant. A diffusion-limiting membrane, held in place and
protected by a mesh, separates the receiving phase from the solution
it is to test. The whole device is suspended, membrane downwards
to protect from fouling, in the test solution. The membrane must
be chosen according to the type of pollutant that is being measured
- inorganic, polar or non-polar organic. The receiving phase has
a very high affinity for the pollutant substance while the membrane
prevents it from becoming saturated too quickly.
To reach the receiving phase, the pollutant
must diffuse through the membrane. The driving force for diffusion
is the concentration outside the membrane, because the concentration
inside is zero as any pollutant inside will immediately be taken
into the receiving phase. The amount taken into the receiving phase
is then extracted with an acid (inorganics) or an organic solvent
(organics), and measured. The system can be calibrated in the laboratory
for a given receiving phase and membrane, using solutions of known
concentrations. The amount of water sampled over time is independent
of external concentration, and once measured for any pollutant this
can be used to determine unknown concentrations in the field. "The
system will not measure such low concentrations as some other existing
devices," says Richard Greenwood, "but the group is more interested
in making sure that high levels are not missed, which is of concern
to legislators and water supply managers."
||The system in
Trials have been carried out comparing the passive
sampling method with spot sampling in a variety of sites in different
countries, including the Rhine near the Dutch border, storm water
in Gothenburg, and two seawater marinas in the UK. In the latter,
measurements were made of two herbicides used in ship antifouling
paints. In open water, levels were extremely low, but within closed
lock gates they were high - concentration of pollutants and accumulation
in the sampler are affected by water turbulence and by temperature.
The group is now hoping to carry out further
development work to look at determination of a wider range of pollutants.
Priority pollutants tend to change over time. Currently, problem
substances include detergents, perfumes, fabric conditioners and
endocrine disrupters. The partnership now holds a UK patent for
the design of the device and its use for non-polar pollutants. For
further work on polar pollutants, the group is seeking a licensing
agreement with other workers researching similar systems, and now
hopes to set up manufacturing arrangements with a company active
in environmental monitoring.