Urban biogeochemistry of labile Hg by diffusive gradients in thin-films technique in anthropogenically-impacted freshwater environment (Zenne River, Brussels)

Activity: Talk or presentationTalk or presentation at a conference


Urbanisation, hydrological engineering and land-use change disrupt natural
biogeochemical cycling of toxic and non-toxic substances alike. Mercury
(Hg) causes health concerns in urban environments due to its past
and present anthropogenic emissions. Its environmental cycle is controlled
by redox, organic matter and microbial reactions, which differ in
heavily urbanised areas compared to natural environments. Knowing the
concentration of the labile (a proxy for bioavailable) Hg fraction becomes
important to understand how, where and when the bioaccumulative
methylmercury (MeHg) is formed. The labile MeHg fraction may be then
subjected to processes leading to enhanced exposure and bioaccumulation
with damaging consequences to human and ecosystem health.
We have investigated Hg species lability with Diffusive Gradient in Thin
films (DGT) technique in surface water and sediment of the Zenne River
(Brussels, Belgium). Labile Hg and MeHg species concentrations indicated
seasonal behaviour in both environmental compartments. The
seasonality depended on the proximity to urbanized areas. Higher labile
Hg concentrations (8.2 ng/L) in surface water in colder season was likely
due to increased emission/deposition via incineration for transport and
household heating. Higher MeHg concentration (2.3 ng/L) was observed
in the beginning of the warmer season and was more pronounced away
from heavily urbanized area. This suggested that although urban-released
Hg is chemically labile, its conversion to the MeHg is likely more
microbially controlled by temperature and not by precursor availability.
Sediment pore waters featured an active labile MeHg profile in the
warmer season with a subsurface peak (5 ng/L), which was absent in
the colder months. Sediments also appeared to be a source of labile
MeHg and THg to the water. Finally, there is an intensive transformation
occurring in the Zenne, and our results clearly indicate the lack of data
and understanding of labile Hg urban biogeochemical cycling, including
the sources, spatial distribution and fate of Hg species. In the absence
of clearly defined point sources, the transported labile Hg species may
create the so-called “halo effect” where Hg impacts ecosystems far from
its point of origin in the urbanized Brussels Area. As the urbanised areas
undergo significant changes in size, demographics, mass and energy
flows, and the temperature stress increases due to global change,
there are many unknowns left about the impact of the sources, sinks and
transformation hotspots of Hg urban biogeochemistry.
Period12 Sep 2019
Event titleInternational Conference on Mercury as a Global Pollutant 2019
Event typeConference
Conference number14
Degree of RecognitionInternational