This document summarizes a study on the impact of persistent organic pollutants (POPs) regulated by the Stockholm Convention in gull eggs from the Ebro Delta Natural Park in Spain. The study evaluated POPs levels in eggs of two gull species, Larus michahellis and Larus audouinii, from 2009-2015. Results showed decreasing trends in PCBs and increases in pesticides like DDE over time. Total POP levels were higher in L. michahellis eggs and may be affecting the birds' condition and the declining population of L. audouinii. The gulls are useful bioindicators for assessing contamination in this protected wetland area impacted by historical industrial pollution.