An assessment of two decades of trace metals monitoring in wild mussels from the Northwest Atlantic and Cantabrian coastal areas of Spain, 1991–2011

• Distributions and trends of metals in mussels are defined after 20 years of study.
• Hg and Pb levels are highest in the Cantabrian region, Cd is affected by upwelling.
• Improved environmental conditions along the northern coasts of Spain are evident.
• In general, detected concentrations do not represent a risk to human health.

Since 1991, the Instituto Español de Oceanografía has monitored the concentrations of trace metals in wild mussels from the north (Cantabrian Sea) and northwest (Atlantic) coasts of Spain to define geographical distributions and temporal trends. While Cu, Zn and As concentrations presented fairly uniform geographical distributions, Hg and Pb concentrations were higher in mussels from the Cantabrian sea region as a result of historical anthropogenic activities. Cd, on the other hand, appeared to be more affected by natural processes on the northwest Atlantic coast (i.e., upwelling) than by human activity. Approximately 70% of the paired observations showed downward trends, 50% of these significant, with time. An improvement in environmental conditions along the northern coasts of Spain is evident despite that some metal levels resulted above the Background Assessment Concentrations given by OSPAR to assess potentially harmful occurrences.