DEPOSITION OF XENOBIOTIC SUBSTANCES BY IR RIGATION WATER FROM THE LABE RIVER

Of surface waters used in tile Czech Republic for irrigation, water fr om the Labe river is the greatest risk of soil and crops contamination by some xenobiotic, particularly organic substances. That is why, in the years 1991 to 1994 within the solution of the project Healthy Nutr ition by the Ministry of Economy of the Czech Republic an extraordinar y attention was paid to the quantification of deposition of xenobiotic substances (XL) by water irrigation from this river. XL depositions p resented in this contribution are calculated for two characteristic pr ofiles of Labe (Vary and Jirice) from average content of these substan ces in water in the vegetation period of 1984 and irrigation quantitie s for crops as determined by Slavik (1994). Deposition of some importa nt XL by irrigation water from Labe of the profile Vary and Jirice in decisive dry year is presented in Tabs II, III, IV. Deposition of xeno biotic organic volatile substances (XOL) differs most between these tw o profiles in view of the quantity - roughly by one to two orders. Of hazardous elements mercury and cadmium were deposited in the lowest qu antity by irrigation water, of XOL substances with higher boiling poin t. Annual deposition of cadmium by water from Labe ranges in tenths g. ha(-1). The same applies to dichlorophenols whose concentrations in La be were highest of al XOL substances with higher boiling point. Of vol atile XOL in the Melnik region most dichlorobenzenes (as much as sever al g.ha(-1)) are deposited by Labe water. In quantities deposited by i rrigation water from Labe, namely from the Vary profile, XL had no mea surable negative effects on soil and quality of crops. They were prove d neither by their analyses (Zavadii, 1992, 1993, 1994a, b), nor by th e examination for genotoxicity by Ames' tests (Cerna, Zavadii, 1994). Soil and crop samples, however, were taken from plots irrigated for 20 to 30 years by high doses of Labe water. Vegetation pot trials with w ell water artificially contaminated by XOL performed at the Research I nstitute of Soil and Water Conservation Praha (Zavadil, 1993, 1994a, b ) showed that their contents in soil increases at a dose of 1 to > 10 kg.ha(-1) (especially in dependence on the type of substance). These X OL doses are many limes higher than those originating from irrigated w ater, namely also during their sampling from Labe in profile of Valy. Deposition of individual XL by irrigation water from from Labe in deci sive dry year, presented in this paper, is lower in an average year. T his is significantly reduced by accumulation of water before its use f or irrigation. In its usage a part of XL is deposited into sediments a nd volatile substances from water are weathering The above findings co rrespond to the present degree of knowledge of XL effect on animals an d environment and present sensitivity of analytical and testing method s. It cannot be eliminated that XL deposition by irrigation water from Labe will be more significant in some aspects in the future than repo rted now.