Probabilistic risk assessment and risk mapping of metals in tropical estuarine sediments using the 1 quarisk model

  • Edem MahuEmail author
  • Elvis Nyarko
  • Daniel Asiedu
  • Wahab Sowah Laryea
  • Ron Szymczak
  • John Twining


Total sediment concentrations of Cd, Cu, Pb, Zn, As, and Hg obtained from the Ankobra, Sakumo II, and Volta estuaries in Ghana were used to generate contaminant probability density distributions and species sensitivity distributions in AQUARISK. Results of the tier 1 assessment showed Cu, Cd, Zn, and Pb were not of concern in the Ankobra as their measured values and the 99th percentile of the fitted distributions were lower than the SQG low-trigger values. Mercury (Hg) and As were however, identified to be of concern in this estuary. In the Sakumo II estuary, Cu, Cd, Pb, and Hg have been identified to be of concern because their concentrations are higher than the SQG low-trigger values. Hg has been identified as the only metal of concern in the Volta estuary. The total proportion of species likely to be affected by the combined concentration of Cd, Cu, and Zn measured from Ankobra, Sakumo II, and Volta were 14%, 16%, and 12%, respectively, according to the Bur III distributional analysis of the ecotoxicology data. The measured median sediment concentrations of As and Hg in the Ankobra estuary greatly exceeded the median sediment concentration targets to achieve a 5% or less exceedence of the SQG low value. Similarly, in the Sakumo II estuary, the measured median sediment concentrations of Cu, Pb, and Hg greatly exceeded the median sediment concentration targets to achieve a 5% or less exceedence of the SQG low. For the Volta estuary however, other metals except Hg fall below the target values.


Ghana Ecotoxicology Probability density distribution Species sensitivity distribution 



The authors would like to thank the International Foundation for Science (IFS) for awarding grants (IFS grant No. W/5331-1) and the International Atomic Energy Agency’s RAF7009 project for providing training on the AQUARISK software. We are also grateful to the following technicians at the Department of Marine and Fisheries Science of the University of Ghana; Mr. Emmanuel Klubi, Mr. Mario Boateng, and Mr. Kofi Enyan who assisted in the collection of samples for the study.


This study was funded by the international Foundation (grant number W/5331-1) and the International Atomic Energy Agency (IAEA grant No. RAF7009).

Compliance with ethical standards

Conflict of interest

Edem Mahu received research grants from IFS. Elvis Nyarko received grants from IAEA part of which provided training on the AQUARISK software.

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors.


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Copyright information

© Springer Nature Switzerland AG 2018

Authors and Affiliations

  1. 1.Department of Marine and Fisheries SciencesUniversity of GhanaAccraGhana
  2. 2.Department of Earth SciencesUniversity of GhanaAccraGhana
  3. 3.Institute for Hydraulic and Coastal EngineeringUniversity of Applied SciencesBremenGermany
  4. 4.TradewindsSydneyAustralia
  5. 5.Austral RadioecologyOyster BayAustralia

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