In the present thesis, analytical methods based on gas chromatography coupled with mass spectrometry, both single (GC-MS) or tandem (GC-MS/MS), have been developed and optimized for the detection and quantification of persistent organic pollutants (POPs) such as organochlorinated pesticides (OCPs) and polychlorinated byphenils (PCBs) and emerging pollutants such as organophosphate esters (OPEs), which are currently used as flame retardants, additives and plasticizers. Another family of flame retardants, also classified as POPs, polybrominated diphenil ethers (PBDEs), was also studied and quantified using already optimized and validated methods. The presence of target POPs in environmentally protected areas of the Iberian Peninsula has been evaluated using seagull eggs as bioindicators. Two species, namely yellow-legged gull (Larus michahellis) and Audouin´s gull (Larus Audouinii), have been selected for this purpose. The former is an abundant and widely distributed species with scavenging and opportunistic behavior, while the later is more vulnerable, even though the population is growing during recent years and new colonies are emerging, and showed a strict fish-based diet. Pollution levels detected in gull eggs were dominated by PCBs, followed by various OCPs. Among OCPs, high levels of dichlorodiphenyldichloroethylene (DDE) were found, which is a metabolic and degradation product of dichlorodiphenyltrichloroethane (DDT), a pesticide widely used during the last decades of the 20th century, which showed high toxicity for birds, being able to reduce the reproduction success because it may affect the eggshell thickness and prevent hatching when present at high enough levels. PBDEs were also widespread in the marine environments of the Iberian Peninsula but at lower levels. Audouin´s gull eggs showed higher pollution levels than yellow-legged gulls from the same colonies, suggesting differences in their feeding habits and their bioaccumulation capacity of POPs. In general, Atlantic colonies were less exposed to POPs pollution than Mediterranean ones. POPS and OPEs were also found in soil and sediment samples from four different protected areas in southern China. Protected areas such as national parks and natural reserves are of especial importance to preserve biodiversity and the natural evolution of ecosystems and are supposed to be pristine because human activities are restricted or forbidden within their geographic boundaries. However, OPEs were commonly found in the samples studied, and were the dominant pollutants, probably due to their current use and related to human activities in the surroundings of the protected areas or the touristic activities that take place within these areas. POPs were detected at lower levels than OPEs, but the alfa isomer of hexachlorocyclohexane, as well as the decabrominated PBDE congener, BDE 209, were the most frequently detected pollutants, being widespread in the environment due to their high production and consumption volumes in China during last decades. The occurrence of POPs and OPEs was also evaluated in soils, sediments and free ranged hen eggs collected in Baihe village, Qingyuan County, Guangdong province of China. This is a hotspot for pollution, associated with electrical and electronic equipment waste (e-waste) because several non-formal workshops were set there. The disassembling of e-waste and recovering of valuable metals became the principal economic activity at the end of the last century and beginning of the present century. Non valuable residues, mostly plastics, have been dumped for years in a little pond that was identified as the main source of pollution of the surrounding ecosystem. The migration of OPEs from the plastic dump to the water and their accumulation in the sediment of the polluted pond has been evidenced, as well as the spread of pollution to other water bodies in the same area. Moderate to high environmental risks were estimated for the presence of target pollutants in abiotic matrixes. Human consumption of free-ranged hen eggs from Baihe village was found to be a route of exposure to pollutants through the diet, posing considerable risks to human health regarding the levels of PCBs and PBDEs found.