Qualitative and quantitative analysis of organochlorine insecticide residues were conducted in water, sediment, aquatic plants and animals from 3 freshwater reservoirs. Ninety water samples, 90 sediment samples, 397 aquatic plants samples and 121 aquatic animals samples were collected during March-April and August-September 1989. There were about 14 kinds of aquatic plants, such as water hyacinth, water lettuce, algae and water lilly etc. Aquatic animals are fish, shrimps and snails, but most of them are fish. They are striped snake-head fish, carp and catfish etc. Total samples of 698 were analyzed by using gas chromatographic techniques at Agricultural Toxic Substances Division. The results indicated that 5 kinds of insecticides were found in most samples. They were lindane, heptachlor, aldrin, dieldrin, DDT and derivatives. Dieldrin was detected at higher concentration and found in all samples. The residue level of dieldrin ranged from 0.01-0.12 ppb in water, 0.005-0.036 ppm in sediment, 0.001-0.138 ppm in aquatic plants and 0.001-0.037 ppm in aquatic animals respectively. The accumulation of dieldrin residue in water and aquatic plant samples from all reservoirs are not different but the level of dieldrin residue in sediment samples from Bueng Boraphed is higher than the other 2 reservoris. However the levels of dieldrin residue in sediment, aquatic plant and aquatic animal samples higher than those in water samples respectively.

The influence of water content and water activity (a sub(w)) on the concentration of volatile compounds in the head-space vapour over model and food samples was studied. Starch-water model systems and three different food systems (hard cheese, apple puree and raw ham) were prepared with a sub(w) values ranging from 0 to 1. For each sample gas chromatographic analyses of volatiles in the headspace vapour and water activity measurements were carried out. For solid foods at intermediate a sub(w) values the highest volatile concentration in the headspace strongly depended on the availability of water. The head-space volatile concentration decreased rapidly when the water became totally free and the water vapour pressure was close to that of pure water | E' stata studiata l'influenza del contenuto in umidita' e dell'attivita' dell'acqua (a inf(w)) sulla quantita' delle sostanze volatili presenti nel vapore dello spazio di testa di sistemi modello e di alimenti aventi una attivita' dell'acqua nell'intervallo di valori di a inf(w) tra 0 e 1. Sui campioni posti in recipienti chiusi ermeticamente sono state determinate per via gascromatografica le sostanze volatili nello spazio di testa e l'attivita' dell'acqua. La concentrazione delle sostanze volatili nello spazio di testa e' risultata fortemente influenzata dalle proprieta' di adsorbimento dell'acqua da parte delle diverse matrici alimentari. La presenza di sostanze volatili e' stata riscontrata al massimo livello, in tutti i casi esaminati, in corrispondenza dell'inizio del ramo ascendente della isoterma di adsorbimento dell'acqua, per discendere rapidamente ai valori piu' elevati di a inf(w), oltre i quali l'acqua presente nell'alimento diviene totalmente disponibile per agire come solvente