Metals in sediments of pore waters of small rivers of St. Petersburg and risks of secondary pollution

The main distribution patterns of metals and metalloids (MM - Sc, V, Cr, Fe, Mn, Zn, Cu, Ni, Co, Pb, Cd, Sr, Ba, Sb, As, Hg) in bottom sediments (BS) and pore waters of small rivers of St. Petersburg affected by industrial wastewater discharges were studied. MM concentrations in solid and liquid phases of bottom sediments (BS) exceed background values by n 10-10 times. The leading influence of chemical specialization of enterprises on their composition was shown. The Pb content in pore water near the wastewater discharge from lead-acid battery production in the Yekateringofka River reached 14.5 mg/l, and the Ni concentration was 8.56 mg/l under the influence of Ni-Cd battery production (Karpovka River). Using correlation, factor and cluster analyses, a relationship was established between the MM content in BS and pore water and complete identity of the main paragenetic associations. The risks of secondary pollution of rivers were established: diffusion flows from BS into water and opening of the pore space during bottom cleaning operations. Based on Fick’s law, the intensity of MM diffusion flows (μg/m day) was estimated, the maximum average values of which are characteristic of Fe (9985), Ba (322), Zn (169), Mn (131), the minimum are typical for As (0.9), Cd (2.4), Co (4.4). Calculations showed that in most cases the intensity of secondary pollution through diffusion input of pollutants prevails over mechanical pollution.