PCDD/Fs and dl-PCBs were determined in gull eggs from 5 Natural Parks in Spain.
Colonies located near to industrial and urban areas presented the highest POP concentrations.
Different POP concentrations were found in cohabitant gull species in Ebro Delta.
Dietary gull habits affect the PCDD/F and dl-PCB occurrence.
Fish eating species presented the highest dl-PCB concentrations.
The aim of this study was to evaluate the presence and distribution of polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/Fs) and biphenyls (PCBs), concretely those so-called as dioxin-like PCBs, in yellow-legged gull eggs (Larus michahellis) collected from five Natural Parks (some of them National Parks) in Spain during the period 2010–2013. PCDD/Fs and dl-PCBs were detected in all the samples. Due to the proximity to important urban and industrial areas higher concentrations were determined in colonies located in the Northern Mediterranean coast than those found in the Southern Mediterranean or Atlantic colonies where a softer anthropogenic impact occurs. Mean ∑ PCDD/F concentrations ranged from 49 to 223 pg/g lipid weight (lw) and ∑ dl-PCB concentrations varied from 146 to 911 ng/g lw. In the Natural Park of the Ebro Delta (Northern Mediterranean coast) two gull species share habitat: yellow-legged and Audouin gull (Larus audouinii). Eggs from both species were collected and PCDD/F and dl-PCB levels compared. The species that feeds exclusively on pelagic fish (L. audouinii) had significantly higher PCDD/F and dl-PCB levels than the scavenger L. michahellis, pointing out the diet-dependent differences in the accumulation of persistent organic pollutants between similar cohabitant breeding species. Finally, mean TEQ values were in general below those considered as critical for toxicological effects in birds.