The aim of this article was to evaluate the influence and effects of chosen bioaccumulative substances i.e. heavy metals, pesticides, and polychlorinated biphenyls (PCBs) on fish, as well as provide information on time trends and potential threat to human health. Chemical substances which pollute water may affect living organisms in two ways. First of all, large amounts of chemical substances may cause sudden death of a significant part of the population of farmed fish, without symptoms (i.e. during breakdown of factories or industrial sewage leaks). However, more frequently, chemical substances accumulate in tissues of living organisms affecting them chronically. Heavy metals, pesticides, and polychlorinated biphenyls are persistent substances with a long-lasting biodegradation process. In a water environment they usually accumulate in sediments, which makes them resistant to biodegradation processes induced by, e.g., the UV light. These substances enter the fish through direct consumption of contaminated water or by contact with skin and gills. Symptoms of intoxication with heavy metals, pesticides, and PCBs may vary and depend on the concentration and bioavailability of these substances, physicochemical parameters of water, and the fish itself.

An investigation on certain bacterial contaminants of Mortadella produced by three Palestinian factories has been carried out. One sample (2units) was taken monthly (June/1999-may/2000) from each of three local factories (A, B&C). The lowest viable bacterial count recorded was 1x 103 CFU/g. in sample No. C1, while the highest count was 3x107 CFU/g. in sample No. B5. Some bacterial strains were isolated during the course of this study by using specific isolation media. They were identified and distributed as: Salmonella spp. (40%) (S. typhi, 6 strains, S. arizonae, 4 strains and S. infantis, 2 strains), Eschirichia spp. (50%) (E. coli, 8 strains and E. coli O157:H7, 7 strains), anaerobic Streptococcus parvulus (3.3%) (One strain) and Clostridum spp. (6.7%) (Cl. baratii, one strain and Cl. botulinum, 2 strains). Three samples (A1, C3 and B10) were mix contaminated; two pathogenic bacterial strains were isolated from each. All investigated samples were negative for Yersinia spp. and Campylobacter spp. The scientific and medical importance was discussed.