Heavy metal concentration in South Vietnam waters

Data obtained from investigations which had been carried out during 1998-1999 in the waters of South Vietnam indicate that concentrations of Fe and Zn were usually higher than permissible limits. In the East South Vietnam waters, Fe concentration varied from 77 to 4450g/l (mean 1045g/l) and Zn concentration varied from 7.24 to 74.1g/l (mean 26.7g/l), Pollution coefficients of the two metals were 10.4 and 2.7 respectively. In the Gulf of Thailand, variation range of Fe was 133-850g/l (mean 318g/l) and of Zn was 4.8-167.8g/l (mean 23.46g/l); corresponding pollution coefficients were 3.2 and 2.3. Mn, Cu, As had mean concentrations lower than permissible limits. In the East South Vietnam waters, variation range for Mn was 9.0-444.6g/l (mean 57.0g/l), for Cu was 1.0- 20.3g/l (mean 3.1g/l) and for As was 1.0-10.5 g/l (mean 3.7 g/l). In the Gulf of Thailand, Mn concentration varied from 1.2 to 410.5g/l (mean 19.1g/l), Cu concentration varied from 1.2 to 14.7g/l (mean 3.7g/l), variation range of As concentration was 1.0-13.3g/l with the mean value was 3.6g/l. Scarce data relating to Hg, Cd, Pb showed that their concentrations in the East South Vietnam waters were negligible (usually < 1.0g/l).

Preservation of cotton fish net twines by tanning 1. Optimum concentration of tanning

Samples of tannin-containing preservatives used by fishermen in India for treating cotton nets were collected and qualitative and quantitative characterisation of the tannins made. The concentrations of different tannins required to impart optimum periods of preservation to the net were worked out and found to be 2% in 8 out of 10 materials studied.

On the measurement of concentration of blanching brine by electrical conductivity method

Blanching is an important operation in the shrimp canning process, in order to bring down the moisture content of the product to the required level, to allow the proteins to coagulate and to give proper texture, shape and characteristic pink colour to the meat. It has been observed that among other factors responsible for fluctuations in the drained weight in the canned prawns, concentration of brine used for blanching and the duration of blanching are important (Varma, Chaudhury and Pillai 1961). The papers gives details of experiments