Assessment of wet weather impact on clam (Chamelea gallina) faecal contamination in the district of San Benedetto del Tronto (Italy)

Since 1998 clams (Chamelea gallina) from the production areas of the district of San Benedetto del Tronto (South Marche - Italy) have been periodically monitored to check the microbiological quality by the detection of the faecal indicator E. coli (MPN method). Results have been inconstant. They were not directly related to contamination sources identified by means of a Sanitary Survey. This one included a desk-based study of the physical, geographic, demographic and urban features of the district above and a shoreline survey to confirm or update previously identified sources. With regard to this, several authors found out that meteoric events, in particular rainfalls, increase faecal loading in marine coastal water. This study investigated the impact of rainfalls on E. coli values in clams from the district of San Benedetto del Tronto according to the sampling plan from 2002 to 2011. The study focused on rainfalls occurred until 4 days before mollusc sampling and set up E. coli values into satisfactory and unsatisfactory levels compared to the food safety limit of 230 MPN/100 g. Data were processed by a statistical tool, the Fisher’s exact test. Results revealed the association between precipitations and exceeding values of E. coli in clams collected from coastal waters of most populous areas to be statistically significant.