Persistent organic pollutants (POPs) are complex organic substances that have toxic properties, are resistant to degradation, accumulate in the environment, are transported by air, water and migratory species across international borders and are stored away from their place of origin. Exposure to persistent organic pollutants can cause serious health effects. Organochlorines (Ocs) are chlorinated compounds widely used as pesticides and are included in the category of persistent organic pollutants. Some of the most toxic organochlorine compounds are polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCH), aldrin, dildrine, dichloro-diphenyl-tetrachloroethane (DDT), heptachlor, etc. The main sources of pollution are agricultural practices, storage of polluted waste in landfills, companies that synthesize these compounds, or power energy installations and condensers containing contaminated oils. Many of the pesticides are considered disruptors of endocrine function in both humans and animals / birds. Although they have been phased out due to their harmful effects, many of these pesticides are still detected in the environment. Concentrations of pesticides and other persistent organic substances are found in most water basins, rivers, seas and oceans. Depending on the 119entra-chemical properties, the contaminants that reach the aquatic environment either remain in the aqueous phase or reach the level of sediments. Thus, for hydrophobic compounds, determining their concentration in sediments describes the distribution of contamination much better than analyzing them in the water column. At sediment level, pesticide-mediated changes can adversely affect the functioning of the ecosystem if tolerant microorganisms cannot compensate for the loss of functionality associated with pesticide-sensitive microorganisms. Moreover, changes in microbial communities can affect the quality and quantity of resources available for aquatic food chains. In Danube Delta, for the monitored sites, the concentrations of total organochlorine compounds varied between 0.282 μg kg-1 and 46 μg kg-1. Among the monitored chlorinated organic compounds, the highest concentrations were determined for the isomers of hexachlorocyclohexane (HCH) and polychlorinated biphenyls (PCBs). The relatively low values of PCBs in the collected samples from the Danube Delta may be due to the fact that these compounds have been used quite little in Eastern European countries. In most lakes and sediments, the concentrations of HCH isomers were on average <0.2 μg kg-1. In the Caraorman Basin, the concentration of γ-HCH (Lindane pesticide) was 8.79 μg kg-1, while in Lake Crișan was detected β-HCH in a concentration of 35.58 μg kg-1 and ε-HCH in a concentration of 1.99 μg kg-1. PCB concentrations were on average <0.5 μg kg-1, except for Lake Crișan where higher concentrations of PCB 101 (2.15 μg kg-1), PCB 138 (2.10 μg kg-1) and PCB 153 (2.80 μg kg-1) were determined. Regarding the insecticide DDT (Dichloro-Diphenyl-Trichloroethane) and its degradation products, relatively low concentrations were determined in the sediment samples, between 0.1 μg kg-1 and 0.78 μg kg-1.