The sources of heavy metals to a wastewater treatment plant was investigated. Sources
can be actual goods, e.g. runoff from roofs, wear of tires, food, or activities, e.g.
large enterprises, car washes. The sources were identified by knowing the metals content
in various goods and the emissions from goods to sewage or stormwater. The sources
of sewage water and stormwater were categorized to enable comparison with other research
and measurements. The categories were households, drainage water, businesses, pipe
sediment (all transported in sewage water), atmospheric deposition, traffic, building
materials and pipe sediment (transported in stormwater). Results show that it was
possible to track the sources of heavy metals for some metals such as Cu and Zn (110
and 100% found, respectively) as well as Ni and Hg (70% found). Other metals sources
are still poorly understood or underestimated (Cd 60%, Pb 50%, Cr 20% known). The
largest sources of Cu were tap water and roofs. For Zn the largest sources were galvanized
material and car washes. In the case of Ni, the largest sources were chemicals used
in the WTP and drinking water itself. And finally, for Hg the most dominant emission
source was the amalgam in teeth. For Pb, Cr and Cd, where sources were more poorly
understood, the largest contributors for all were car washes. Estimated results of
sources from this study were compared with previously done measurements. The comparison
shows that measured contribution from households is higher than that estimated (except
Hg), leading to the conclusion that the sources of sewage water from households are
still poorly understood or that known sources are underestimated. In the case of stormwater,
the estimated contributions are rather well in agreement with measured contributions,
although uncertainties are large for both estimations and measurements. Existing pipe
sediments in the plumbing system, which release Hg and Pb, could be one explanation
for the missing amount of these metals. Large enterprises were found to make a very
small contribution, 4% or less for all metals studied. Smaller enterprises (with the
exception of car washes) have been shown to make a small contribution in another city;
the contribution in this case study is still unknown.