Estuarine pollution imposes rapid, increasing and lasting environmental modifications. In the present review, especial
attention is given to estuaries in South America (SA), where legislation, policies and actions to guarantee environmental quality remain ineffective. There, the majority of estuaries face uncontrolled occupation of its margins by urban and industrial centres, agriculture and aquaculture expansion, water extraction and flow control.
The lack of basic sanitation and poor environmental management (including territories within Marine Protected Areas) often lead to hydrological alterations, high nutrient loads, and the presence and dynamics of pollutants (nutrient loads, persistent organic pollutants (POPs), metals and plastic debris) along the entire estuarine
ecocline.Organic enrichment has increased dissolved oxygen consumption, withwide spatio-temporal variability
along latitudes and estuarine gradients. The toxicity, biogeochemistry and availability of metals and POPs depend on the annual fluctuations of salinity, water renewal, dissolved oxygen levels, suspended particulate loads, sediment mobility, grain size and composition at the sink. Plastic debris from land sources are widespread
in estuaries,where they continue to fragment into microplastics. River basins are themain contributors of plastics to estuaries, whose transportation and accumulation are subjected to interannual water flow variations. Although some systems seems to be in a better condition in relation to others around the world (e.g. Goiana and
Negro estuaries), many others are among the most modified worldwide (e.g. Guanabara Bay and Estero Salado
System).We propose that, estuarine conservation plans should consider year-round fluctuations of the ecocline
and the resulting cycles of retention and flush of environmental signals and their influence on trophic webs over the whole extent of estuarine gradients.