Augusta bay, in south of Italy, is described as one of the heavy polluted regions in the Mediterranean Sea, with different pollutants, including mercury. Several sampling campaigns were conducted in the bay to measure the mercury concentrations in different environmental media. In order to quantify and assess the severity of the mercury pollutant and its impact on fish then possibly transferred to human, a preliminary risk assessment was needed. The data for the seawater, sediments and the sediment-seawater interface were obtained from previous studies. Mercury concentration in sea water was used in this study. The data were divided into three layers according to the depth, surface layer has depth from the surface to 10 m below the sea surface, middle layer from 10 – 20 m and the bottom layer from 20 m to the sea bottom. A total of 22 stations were measured, 18 stations inside the bay and 4 stations outside the bay. The modelling was done in a GIS environment using ArcMap 10.5. The data were first examined to ensure their validity to be used in GIS, by simply checking the distribution of the data by histograms and Q-Q plots. In order to predict the concentration in un-sampled areas, the fate and distribution of the mercury concentration, the spatial continuity of the concentration was performed and checked by semivariogram models for the three layers. The models were cross-validated as well as the errors of the models estimated. After the spatial continuity of the models were checked and validated, the kriging models were produced and resulted in Hg maps for each layers. The data were then used to perform the risk assessment based on hazard quotient calculation. The water concentration was, in fact, used to obtain the concentration in fish based on a bioaccumulation screening model, requiring the bioconcentration factor of mercury and seawater concentration as inputs. The concentration of mercury in fish was calculated in each zone of the bay and it was used to calculate the dose for fish consumption. This model has identified some zones as hazardous zones for human consumption, which it confirmed the righteousness of the decision of the Italian authorities to interdict the fishing activity in the bay since 2007. The aim of the work was to propose a simple and preliminary risk assessment model, to be used even at the initial stages of characterization of contaminated sites, to highlight the most critical areas and to guide subsequent remediation actions.
La baia di Augusta, nel sud dell'Italia, è descritta come una delle aree più inquinate nel Mar Mediterraneo, con diversi inquinanti, tra cui il mercurio. L’area è stata oggetto di varie campagne di caratterizzazione ambientale. Per quantificare e valutare la gravità dell'inquinamento da mercurio e in particolare il bioaccumulo nei pesci in ragione dei rischi per ll'uomo, è stata necessaria una valutazione preliminare del rischio. I dati relativi all'acqua di mare, ai sedimenti e all'interfaccia del sedimento-acqua di mare sono stati desunti da studi precedenti. Dato fondamentale, utilizzato per questo studio, è la concentrazione di Hg disciolta nell'acqua di mare, che è stata divisa in tre strati secondo la profondità, lo strato superficiale fino a 10 m di profondità, uno strato medio da 10 a 20 m, e lo strato inferiore da 20 m fino al fondo marino. Sono stati utilizzati i dati ricavati da 22 stazioni di misura, 18 stazioni all'interno della baia e 4 stazioni fuori dalla baia. La modellazione è stata eseguita in un ambiente GIS utilizzando ArcMap 10.5. I dati sono stati prima esaminati per verificarne la validità per poter essere utilizzati in GIS per le valutazioni successive. Per prevedere la concentrazione in aree non campionate, il destino e la distribuzione della concentrazione di mercurio, è stata controllata la continuità spaziale dei dati di concentrazione attraverso costruzione dei semivariogrammi sperimentali per i tre strati. I modelli sono stati validati, procedendo anche alla stima degli errori. Successivamente si è proceduto all’interpolazione con kriging ricavando mappe delle concentrazioni disciolte di Hg nella baia in funzione delle profondità. Tali mappe sono state utilizzate per eseguire la valutazione dei rischi. La concentrazione dell'acqua è stata, infatti, utilizzata per ottenere la concentrazione nel pesce attraverso un modello di screening di bioaccumulo; utilizzando come dato di input la concentrazione di Hg disciolto e un fattore di bioconcentrazione di letteratura, è stato possibile stimare la concentrazione di mercurio attesa negli organismi acquatici in ciascuna zona della baia. Questa informazione è posi stata impiegata per la valutazione dell’esposizione e la stima del rischio. Nello specifico all’interno della baia sono state identificate alcune aree con rischio elevato per consumo umano di pesce, fatto che giustifica a pieno la decisione delle autorità italiane di interdire l'attività di pesca nella baia dal 2007. L'obiettivo del lavoro è stato quello di proporre un modello semplice e preliminare di valutazione del rischio, da impiegare anche nelle fasi iniziali di caratterizzazione dei siti contaminati a mare, per evidenziare le aree più critiche e guidare le successive azioni di bonifica.
Methylmercury risk assessment using a GIS model : the case study of Augusta Bay (Sicily)
ELWALEED AHMED IBRAHIM, AHMED
2016/2017
Abstract
Augusta bay, in south of Italy, is described as one of the heavy polluted regions in the Mediterranean Sea, with different pollutants, including mercury. Several sampling campaigns were conducted in the bay to measure the mercury concentrations in different environmental media. In order to quantify and assess the severity of the mercury pollutant and its impact on fish then possibly transferred to human, a preliminary risk assessment was needed. The data for the seawater, sediments and the sediment-seawater interface were obtained from previous studies. Mercury concentration in sea water was used in this study. The data were divided into three layers according to the depth, surface layer has depth from the surface to 10 m below the sea surface, middle layer from 10 – 20 m and the bottom layer from 20 m to the sea bottom. A total of 22 stations were measured, 18 stations inside the bay and 4 stations outside the bay. The modelling was done in a GIS environment using ArcMap 10.5. The data were first examined to ensure their validity to be used in GIS, by simply checking the distribution of the data by histograms and Q-Q plots. In order to predict the concentration in un-sampled areas, the fate and distribution of the mercury concentration, the spatial continuity of the concentration was performed and checked by semivariogram models for the three layers. The models were cross-validated as well as the errors of the models estimated. After the spatial continuity of the models were checked and validated, the kriging models were produced and resulted in Hg maps for each layers. The data were then used to perform the risk assessment based on hazard quotient calculation. The water concentration was, in fact, used to obtain the concentration in fish based on a bioaccumulation screening model, requiring the bioconcentration factor of mercury and seawater concentration as inputs. The concentration of mercury in fish was calculated in each zone of the bay and it was used to calculate the dose for fish consumption. This model has identified some zones as hazardous zones for human consumption, which it confirmed the righteousness of the decision of the Italian authorities to interdict the fishing activity in the bay since 2007. The aim of the work was to propose a simple and preliminary risk assessment model, to be used even at the initial stages of characterization of contaminated sites, to highlight the most critical areas and to guide subsequent remediation actions.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/134608