Mercury distribution in estuarine environments from Argentina: the detoxification and recovery of salt marshes after 15 years

Abstract

Total Hg contents from abiotic (surface sediments and suspendedparticulate matter) and biological (crabs, fishes and halophytes)compartments from Bahía Blanca estuary and Mar Chiquita CoastalLagoon, Argentina, have been monitored since the 1980's. At BahíaBlanca estuary, high Hg concentrations were recorded during the early1980's in surface sediments (0.34 ± 0.22 μg/g) andsuspended particulate matter (0.19 ± 0.10 μg/g). Fishspecies, Mustelus schmitti (0.89 ± 0.29 μg/g), Paralichthys brasiliensis (0.85 ± 0.18 μg/g) and Micropogonias furnieri (0.37 ± 0.11 μg/g) also presentedhigh Hg concentrations. The large industrial nucleus located within theestuary has been identified as the main metal source for this environment.Hg contents from the same area during 1996–1998 were significantlylower: surface sediments (0.164 ± 0.023 μg/g), suspendedparticulate matter (0.048 ± 0.0017 μg/g), fish Micropogonias furnieri (0.13 ± 0.02 μg/g) and crab Chasmagnathus granulata (0.334 ± 0.071 μg/g). This trendof environmental detoxification is probably related with (i) thetechnological changes incorporated by the local industry, (ii) a mostadequate management of industrial effluents, and (iii) the removal ofgreat sediment volume by dredging and refill.During the 1980's Mar Chiquita Lagoon Hg concentrations reached 0.08± 0.01 μg/g in surface sediments and 0.09 ±0.025 μg/g in suspended particulate matter, and 0.14 ±0.04 μg/g in the fish Basilichthys bonariensis and 0.22 ±0.08 μg/g in Paralichthys brasiliensis, and 0.08 ±0.01 μg/g in the crab C. granulata, Hg concentrations werelower than at Bahía Blanca. Remote Hg sources for this Coastal Lagoonand atmospheric and stream transport of Hg is proposed as major Hgsources, since no Hg point sources exists nearby. Mercury concentrationsrecorded in the 1996–1998 period were lower than those recorded inthe previous decade: surface sediments (0.019 ± 0.004 μg/g), suspended particulate matter (0.030 ± 0.008 μg/g), halophyte Spartina densiflora (0.013 ± 0.008 μg/g) or crab C. granulata (0.011 ± 0.009 μg/g).Both Hg bioaccumulation and biomagnification processes were verified inBahía Blanca estuary and in Mar Chiquita Coastal Lagoon. This apparentrecovery of both estuarine environments deserves to be carefully analyzed,in order to fully understand the foundations of these processes.