The　biogeochemical　behavior　of　Cd,　Co,　Cr,　Cu,　Ni　and　Pb　along　the　historically　polluted　Scheldt　estuary　(Belgium　-　The　Netherlands)　was　investigated　in　this　study.　As　never　studied　before　in　this　area,　labile　trace　metals　were　measured　using　the　passive　sampling　technique　of　Diffusive　Gradients　in　Thin-films　(DGT),　while　total　dissolved　and　particulate　trace　metal　concentrations　were　assessed　using　classic　active　sampling　techniques.　This　dual　approach　allowed　us　to　highlight　the　variations　of　trace　metal　speciation　and　distribution　in　the　estuarine　surface　waters,　considering　environmental　and　physicochemical　gradients　along　the　transect.The　large　data　set　obtained　was　then　compared　with　literature　data　of　historical　measurements　along　the　Scheldt　(from　1980　until　now),　but　also　from　other　estuaries.　As　emphasized　by　our　results,　trace　metal　mobility　and　partitioning　along　the　Scheldt　estuary　was　mainly　driven　by　biogeochemical　reactions　which　were　strongly　influenced　by　gradients　of　specific　estuarine　physico-chemical　parameters,　such　as　salinity,　turbidity,　temperature　and　so　on.　Hence,　all　species　of　trace　metals　displayed　a　non-conservative　behavior.　More　precisely,　dissolved　labile　fractions　of　trace　metals　showed　higher　levels　in　the　middle　estuary,　where　many　solubilization　and　remobilization　processes　occurred　due　to　turbulent　mixing　mechanisms　and　an　increasing　salinity.　Our　study　confirmed　the　decreasing　trend　historically　observed　for　particulate　metals　along　the　Scheldt,　as　well　as　the　rising　concentrations　recorded　for　dissolved　trace　metals　which　might　also　lead　to　an　increase　of　their　labile　fraction　measured　by　the　DGT.　Finally,　these　preliminary　results　suggested　that　a　more　regular　monitoring　of　labile　metal　along　the　Scheldt　estuary　is　essential　to　have　an　in-depth　understanding　of　trace　metal　speciation　and　to　review　bioavailability　of　trace　metals　within　estuarine　ecosystems.　(C)　2020　Elsevier　B.V.　All　rights　reserved.