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