In 1996 (March and June) the mineral water "Rudovci" was sampled in its spring in the village Rudovci, Serbia (Yugoslavia). The physical-chemical analyses have shown that the temperature of the water was 180 deg C with sodium-carbonate content. It has been considered that the quality of water was variable in a short period from 3 months. Comparing the analyses of the mineral water from 1996, we can consider some remarkably distinctions in some chemical elements. The chemical analyses made in 1996, have shown changes in following contents: magnesium (47.6 and 64.5 mg/l); sodium (1313 and 1355 mg/l); iron (2.35 and 3.76 mg/l); boron (5.2 and 4.8 mg/l); arsenic (0.08 and 0.06 mg/l). In 1974, the chlorine content was 28.4 mg/l, but about 218 mg/l in 1996. The nitrate content varied from high (19.2 mg/l) in 1974 to low (about 0.75 mg/l) in 1996.

Needles of 20 years old spruces from Prednji vrh, in the area affected by the Sostanj power station, and from Pokljuka (Alps region, with a relatively unpolluted environment), were analysed for total sulphur content (St). Measurements were taken in a period between April and August twice monthly and in the period from August to April every four weeks (May 1993 - June 1994). Sulphur content in one and two years old spruce needles from Prednji vrh were much higher (one year old needles 2.06-2.50 mg/g needle dry weight, 1993) than in needle samples from Pokljuka (one year old needles 1.05-1.25 mg/g needle dry weight, 1993).

Investigation in this study should indicate to importance of aquatic macrophytes in accumulation of toxic metals in aquatic ecosystems and control of their pollution, as well as to establish which plants are well hiperacumulators and test species for remediation, in order to protection, regeneration and conservation of the Gruža lake as reservoir that is important for water supply and as particular natural ecosystem. Obtained results showed that species Lemna gibba L. was reliable indicator of surrounding conditions (environment), as well as good accumulator of heavy metals, so it could be used to remediate aquatic ecosystems.