A zinc oxide (ZnO) pilot plant furnace was used to synthesize ZnO nanoparticles at very high capacities in a range of 1-4 t/month. The 4-t custom-designed furnace was used to synthesize ZnO particles possessing primary nanoparticles resembling rods and grains. At a combustion temperature of 1000-1300°C, zinc vapour was oxidized into ZnO powder in order to produce granular ZnO (ZG) particles. By blowing air into the combustion chamber, ZnO nanorods (ZR) were produced. The ZR specimen exhibited higher XRD intensities, stronger photocatalysis and higher electrical resistance compared to that of ZG sample. However, the ZR sample showed a stronger toxicity to marine phytoplankton, Isochrysis galbana, by starting to inhibit cell growth at 8 mg/L ZnO concentration in seawater whereas ZG sample started showing growth inhibition at a higher ZnO concentration of 32 mg/L. The toxicity of ZnO primary nanoparticles was probably attributed to the dissolution, release and uptake of free zinc ions especially for the case of the higher surface area of ZR particles that exhibited relatively higher zinc concentration on the particle surface, based on the elemental mapping of the electron spectroscopy imaging results.
The cockle, Anadara granosa, was experimentally exposed to low (0.1 mg/L) and sublethal (1.0 mg/L) doses of copper (Cu) for a period of 24 hrs. Significant increase in Cu concentrations in whole tissues and hepatopancreas compared to control animals were observed. In order to study the effect of copper exposure at molecular levels, a subtractive cDNA library was constructed from the hepatopancreas of cockles exposed to 1.0 mg/L Cu. Screening of the subtractive cDNA library using reverse northern analysis resulted in several differentially expressed genes, including one that codes for metallothionein (MT). The complete coding sequence of the MT gene (designated as AnaMT2) reveals an open reading frame of 234 bp in length that encodes a 77 amino acid polypeptide as revealed by the deduced amino acid composition. Although showing similarities with other molluscan MTs, AnaMT2 can be distinguished by its lower glycine and higher asparagine and proline content. Expression analysis of the AnaMT2 by northern analysis indicated higher mRNA level in cockle exposed to 1.0 mg/L Cu and was undetectable in those treated with 0.1 mg/L. This suggests that AnaMT2 represents a primarily inducible MT not highly expressed under basal conditions.