RESUMO
The results of the successful implementation of a treatment based on the injection of ozone (O3) and oxygen (O2) into a contaminated body of water are reported for the first time. Three decontaminating units (SCAVENGER™), which have the capacity to inject up to 120 g O3/h and 250 Kg O2/h in the form of microbubbles (90 ± 10 µm in diameter), were placed in the contaminated Valsequillo reservoir, Central Mexico. In order to evaluate the efficacy of the treatment, 20 physicochemical parameters, 18 organic compounds, 66 inorganic compounds and 11 biological indicators were measured before, during and after the treatment; all of them in several representative sites of the east side of the Valsequillo reservoir. After 5 months of operating the SCAVENGER™ units in the eastern part of the reservoir, the concentration of Dissolved Oxygen (DO) increased 68%. Likewise, the chemical reducing conditions of the reservoir reflected by the low oxidation-reduction potential (ORP; -237 ± 75 mV) became quasi-oxidant (10 ± 58 mV). The treatment was efficient in water disinfection, presenting an 80% reduction in Fecal Coliforms (FC). Some heavy metals also showed a decrease in their concentration, being as follows: Al (65%), Cr (35%), Pb (46%), Zn (60%), Mn (20%), Mo (40%), Fe (32%), As (58%) and Co (26%). Due to the selective reactivity of ozone towards aliphatic and aromatic unsaturated compounds, several organic compounds reduced in their concentration by up to two orders of magnitude. Based on the above, it is evident that the treatment with ozone and oxygen was effective in substantially improving the quality of water in the east side of the Valsequillo reservoir.
RESUMO
With the view of using Nucella lapillus and Monodonta lineata as bioindicators in biomonitoring programs in the NW coast of Portugal, the sensitivity to copper and cadmium of these two common species in Atlantic coasts of Europe was investigated. Assays based on mortality and on the activity of the enzymes cholinesterases (ChE) and glutathione S-transferases (GST) were used, as these biomarkers have been used in biomonitoring studies in the area. ChEs present in foot muscle of both species were characterised and found to show properties of both typical acetylcholinesterase and pseudocholinesterase. Cadmium LC50s for N. lapillus and M. lineata were 2.64 and 2.44 mg/L, respectively, while the lowest observed effect concentration (LOEC) was 1.53 mg/L for both species. LOEC value for cooper was 0.075 mg/L for both. Cadmium in vivo exposure increased ChE activity of N. lapillus, but had no effects on M. lineata ChE. No in vitro effects of cadmium on ChE activity of any of the tested species was observed. Copper had no significant in vivo effects on ChE activity, although it inhibited the ChE of both species in vitro, the IC50s being 5.87 and 12.17 mg/L for N. lapillus and M. lineata, respectively. Cadmium had no significant effects on GST activity of either species, while copper caused a significant reduction of N. lapillus GST (LOEC=0.044 mg/L) but had no effect on M. lineata GST. Results indicate that (i) N. lapillus and M. lineata have a similar acute sensitivity to cadmium and copper; (ii) ChE and GST of these species are sensitive to cadmium (iii) ChEs of both species are inhibited by copper at concentrations in the mg/L range and therefore, its use is limited to heavily polluted sites; (iv) N. lapillus GST does not seem to be a suitable biomarker for copper, at least in the range of concentrations tested, since it was inhibited by copper, but no clear concentration-response relationship was observed.
