Variation of zinc concentrations in lake bottom sediments and implications for recreational use of water bodies

Zinc content in bottom sediments was tested in 50 water bodies on the Silesian Upland (southern Poland). The metal was found in concentrations that ranged from 83 mg/kg to 38,400 mg/kg, that is, in amounts not previously found in any other water bodies worldwide (e.g., Hubertus I—38,400 mg/kg, Brzeziny—38,200 mg/kg, Morawa—35,300 mg/kg). It has been established that the bottom sediments of water bodies used for recreational purposes on the Silesian Upland are contaminated with zinc to varying degrees, as evidenced by geoecological indicator values, that is, the geoaccumulation index (−2.2 < Igeo < 8.7), the sediment contamination factor (0.5≤Cfi<219.4), the anthropogenic enrichment factor (1.2 ≤ IAP < 512.0), and the ratio of the concentrations found to the regional geochemical background (0.3 < IRE < 148.3). Zinc contamination of bottom sediments has been caused by human activity, with only minimal influence of natural conditions. The water bodies surveyed overwhelmingly do not meet the geoecological conditions for safely engaging in recreation and leisure activities. A ratio of the concentrations found to the regional geochemical background of IRE ≤ 5.0 has been proposed as the acceptable range for recreational use of water bodies involving direct contact of living organisms with zinc-containing bottom sediments. The need to revitalize, reclaim, and protect the water bodies in question has been pointed out.