Elsevier

Science of The Total Environment

Volume 565, 15 September 2016, Pages 961-976
Science of The Total Environment

Modelling ecological and human exposure to POPs in Venice lagoon. Part I — Application of MERLIN-Expo tool for integrated exposure assessment

https://doi.org/10.1016/j.scitotenv.2016.04.146Get rights and content

Highlights

  • Ecological and human internal exposure to POPs was simulated with MERLIN-Expo

  • A long-term exposure scenario was simulated using 5 models from MERLIN-Expo library

  • POPs measurements in biota and human serum were used to evaluate model performance

  • Simulated internal exposure estimates are in good agreement with biomonitoring data

  • The evaluation of internal exposure estimates against benchmarks showed no significant risk

Abstract

Industrial and urban emissions over several decades left a legacy of contamination by persistent organic pollutants in the sediments of Venice lagoon (Italy), which might still represent a hazard for the health of ecosystems and population. A new modelling tool for integrated exposure assessment, MERLIN-Expo, was applied to simulate integrated ecological and human exposure to PCBs and dioxins. MERLIN-Expo library provides a set of environmental fate models that can be easily combined to create several scenarios, and coupled to a human intake and a physiologically-based pharmaco-kinetic (PBPK) model to simulate human internal exposure. The Phytoplankton, Invertebrate and Fish models implemented in MERLIN-Expo library were combined to create an aquatic food web and to dynamically simulate bioaccumulation and biomagnification of dioxins and PCBs. Concentrations of PCB and dioxins in water, reconstructed from concentrations in dated sediment cores, were used as time-series inputs to run long term simulations. Estimated concentrations in edible aquatic species were used to estimate daily human intake through the consumption of local seafood. Finally, the application of the PBPK model allowed to explore the accumulation of 2,3,7,8-TCDD and PCB126 in human tissues for several decades. Simulated chemical concentrations in biota were evaluated against monitoring data for four aquatic species, finding an appreciable agreement, with some differences depending on the species and target chemicals. Estimated chemical concentrations in blood were compared to real human biomonitoring data measured in adult men. Despite several assumptions included in the assessment framework, simulated concentrations resulted close to measured data (the same order of magnitude or one order of difference). The results allowed performing a preliminary ecological and human health risk assessment for the selected chemicals by evaluating the exposure estimates against benchmark values available in literature. The study provided useful insights for supporting the verification of MERLIN-Expo in a real complex exposure scenario.

Introduction

The lagoon of Venice is a superficial basin, located along the north-western coast of the Adriatic Sea. It can be defined as a transitional environment, characterized by shallow waters (Guerzoni and Tagliapietra, 2006) and influenced by several anthropogenic activities such as industry, fishery, and tourism. These activities have caused in the past and still cause the release in environmental media of a wide range of chemical substances, including persistent organic pollutants (POPs). The most significant sources of POPs can be identified in the industrial area of Porto Marghera (where many chemical industries, oil refining plants, and waste incineration plants were present, today partially dismissed), the treated and untreated municipal wastewater from the city of Venice and surrounding urban centres, contaminant loads from rivers from the catchment area and atmospheric depositions (Collavini et al., 2005, Guerzoni et al., 2005). Lagoon sediments, which keep trace of historical time trends of emissions (Dalla Valle et al., 2005, Frignani et al., 2005), represent the most important secondary source of POPs. Despite the implementation of environmental protection regulations and the application of technologies for emissions control in the last two decades, the affinity of POPs to organic matter and their persistence (Ritter et al., 2007) resulted in a legacy of contaminated sediment in the lagoon of Venice. Due to their resistance to chemical and biological degradation, chemicals like polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) can indeed be detected in environmental matrices for a long time after their production and release and can represent for many years a hazard to ecosystems and human health (UNEP, 2001). POPs are bioaccumulative and can magnify along aquatic and terrestrial food webs, with high exposure potential for top predators (Kelly et al., 2007). Human populations can be exposed to POPs through different pathways, but food of animal origin often represents the most significant sources of POP exposure for humans (Moser and McLachlan, 2002). Therefore, if a comprehensive and realistic risk assessment is pursued, the link between ecosystems' contamination and human exposure should deserve special attention when investigating POP fate and effects.

Considering the persistence of POPs, their potential for bioaccumulation and biomagnification, and the possibility to cause adverse biological effects even long time after exposure, risk assessment of POPs requires approaches and tools adequate to realistically reconstruct long term exposure scenarios, covering many decades or the entire human life span, and able to incorporate at the same time both ecological and human targets. The potentialities of integrating ecological and human exposure assessment, referred to as “Integrated Exposure Assessment”, has been recently highlighted by Ciffroy et al. (2015), who described the benefits of adopting common modelling frameworks, including the development of common exposure scenarios and the harmonization of monitoring and modelling activities covering both the ecological and human health domains.

In recent years several studies focused on modelling bioaccumulation and biomagnification of PCB and dioxins in terrestrial and aquatic ecosystems in different environments by means of food web models, which include several species at different trophic levels. Some examples are provided by Armitage and Gobas (2007), Arnot and Gobas (2004), Figueiredo et al. (2014), Gobas and Arnot (2010), Gobas and Wilcockson (2003), Micheletti et al. (2008) and Nfon et al. (2011).

At the same time, many authors investigated the exposure of human populations to PCB and dioxins through several modelling approaches. Human exposure can be evaluated in terms of “external exposure” (WHO-IPCS, 2005), by combining data on chemical concentrations in contact media (air, soil, water, food) with frequency and duration of contact or food daily intakes and with absorption across the contact surface to estimate the overall daily dose of chemical entering the body. However, in recent years, attention moved towards the estimate of internal exposure, that is the dose to a target tissue or organ, which can be used to characterize more effectively the link between the intake from the environment and the arise of adverse health effects. Pharmacokinetic (PK) models can be developed and applied for this purpose: they describe the fate of chemical compounds in the body by simulating biological processes of absorption, distribution, metabolism and excretion (ADME). More complex models account for organism physiology and can simulate age- and/or gender-dependent changes over time. These models, called physiologically-based pharmacokinetic (PBPK) models, are suitable to predict the determinants of inter- or intra-individual variability on internal dosimetry (Bois et al., 2010).

Several examples of internal exposure modelling for different congeners of PCBs and dioxins are available in literature. Some authors developed and/or applied PK or PBPK models to reconstruct past exposure scenarios or to simulate possible future exposure (Alcock et al., 2000, Bu et al., 2015, Sweetman et al., 2000, Ulaszewska et al., 2012), to explore the linkage between internal exposure and relevant determinants such as age, diet, and reproductive behaviours (Quinn et al., 2010, Quinn and Wania, 2012), to derive POP elimination half-lives (Ritter et al., 2011), or to assess the relationships with variable emissions scenarios or emissions from specific polluting sources (Nadal et al., 2013, Nøst et al., 2015, Schuhmacher et al., 2014).

Only few studies proposed an integrated modelling of ecological and human exposure within a comprehensive assessment. An example is offered by (Czub and McLachlan, 2004), who developed and applied a fugacity-based mechanistic model (ACC-HUMAN) to describe bioaccumulation of lipophilic organic pollutants from air, water and soil to humans, considering aquatic and terrestrial food chain. The model was also coupled to a long-range multimedia fate model by Breivik and colleagues (in the CoZMoMAN model) (Breivik et al., 2010) or to the global transport model Globo-POP (Czub et al., 2008) and further applied in different regional contexts (e.g., Quinn et al., 2010, Quinn and Wania, 2012). However, ACC-HUMAN does not address the kinetic aspects of contaminant distribution in human body (Czub and McLachlan, 2004).

To the best of our knowledge, no previous studies addressed integrated exposure modelling of PCBs and dioxins in the Venice lagoon area. Environmental processes and POP contamination in the Venice lagoon have been the target of different monitoring and research projects and initiatives in the last three decades. Several monitoring campaigns investigated the distribution of PCBs and dioxins in Venice lagoon (e.g., Secco et al., 2005, Venice Water Authority, 1999, Venice Water Authority, 2000a, Venice Water Authority, 2000b) and some studies included the monitoring of chemical concentrations in aquatic species living in the lagoon (e.g., Venice Water Authority, 1999, Venice Water Authority, 2006), but only very few studies investigated the presence of these chemicals in human tissues. Multimedia models and aquatic food web models were applied to explore the fate and transport of POPs in different environmental matrices and bioaccumulation and biomagnification processes along the aquatic food web (Dalla Valle et al., 2003, Micheletti et al., 2008, Sommerfreund et al., 2010). However, a comprehensive modelling of POP behaviour from environmental concentrations to the estimate of human internal concentrations has not been conducted before. Taking into account the toxicity of dioxins and PCBs, which have been associated to several serious health effects, including cancer, birth defect, neurological impairment, sterility, endocrine disruption (ATSDR, 2000, Ritter et al., 2007, Schecter, 2012), and the scarcity of human biomonitoring studies conducted in the area, the potential utility of predictive modelling tools to explore the relationships between environmental contamination distribution, diet patterns and internal exposure is evident.

MERLIN-Expo tool, recently developed in the frame of 4FUN project (www.4funproject.eu), offers the possibility to perform ecological and human exposure modelling on the same platform, providing a library of models which can be flexibly combined to recreate complex exposure scenarios where both ecological and human targets can be included (Ciffroy et al., this issue). MERLIN-Expo allows to dynamically simulate bioaccumulation in different aquatic species and biomagnification along the aquatic food web and, subsequently, to model human chemical intake and internal exposure (concentrations in different tissues and organs) through a generic PBPK model.

The main objective of this work is to simulate ecological and human exposure to PCBs and dioxins in Venice lagoon, and to test the feasibility of reconstructing long term exposure scenarios by applying the new MERLIN-Expo tool. Moreover, the study aims at evaluating the performance of MERLIN-Expo in integrated exposure modelling through the comparison of model results against real monitoring data, including chemical concentrations in target aquatic species and human biomonitoring data collected in the municipality of Venice.

Section snippets

Case study

The lagoon of Venice can be divided into three main basins: southern, central and northern lagoon. For the integrated exposure assessment, the central lagoon has been selected as target area: it is close to Porto Marghera industrial area and has been strongly influenced by discharge of contaminants associated to industrial activities. Many studies on superficial sediments showed that the concentrations of persistent organic pollutants such as dioxins and PCBs in the central basin were higher

Ecological exposure assessment

The aquatic food web models included in MERLIN-Expo provided as output of the deterministic simulation the time trend of concentrations from 1924 to 1998 of all target chemicals in aquatic organisms included in the Venice lagoon food web.

Time dependent concentrations of 2,3,7,8-TCDD and PCB126 in selected species are reported in Fig. 3 and Fig. 4 respectively. Results, expressed on a fresh weight basis, show the highest accumulated concentrations for phytoplankton for 2,3,7,8-TCDD and for T.

Conclusion

The new exposure modelling tool MERLIN-Expo was applied to assess the bioaccumulation and biomagnification of a set of dioxins and PCBs in the aquatic food web of the Venice lagoon and the exposure of local population (high fish consumers sub-group) through the intake of contaminated seafood from the same lagoon. For these purposes, five models from MERLIN-Expo library were combined (Phytoplankton, Invertebrate, Fish, Human Intake and Man models) and deterministic simulations were run for a

Acknowledgements

The research leading to these results has received funding from the European Union's FP7 under the project “4FUN — The FUture of FUlly integrated human exposure assessment of chemicals: Ensuring the long-term viability and technology transfer of the EU-FUNded 2-FUN tools as standardized solution” (Grant Agreement No 308440).

The authors would like to thank Erik Johansson and Boris Alonso (FACILIA) for their valuable technical support in the implementation of the aquatic food web models in

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