Escherichia coli contamination and health aspects of soil and tomatoes (Solanum lycopersicum L.) subsurface drip irrigated with on-site treated domestic wastewater

Anita Forslund, J. H. J. Ensink, B. Markussen, A. Battilani, G. Psarras, S. Gola, L. Sandei, T. Fletcher, A. Dalsgaard

Research output: Contribution to journalJournal articleResearchpeer-review


Faecal contamination of soil and tomatoes irrigated by sprinkler as well as surface and subsurface drip irrigation with treated domestic wastewater were compared in 2007 and 2008 at experimental sites in Crete and Italy. Wastewater was treated by Membrane Bio Reactor (MBR) technology, gravel filtration or UV-treatment before used for irrigation. Irrigation water, soil and tomato samples were collected during two cropping seasons and enumerated for the faecal indicator bacterium Escherichia coli and helminth eggs. The study found elevated levels of E. coli in irrigation water (mean: Italy 1753 cell forming unit (cfu) per 100 ml and Crete 488 cfu per 100 ml) and low concentrations of E. coli in soil (mean: Italy 95 cfu g(-1) and Crete 33 cfu g(-1)). Only two out of 84 tomato samples in Crete contained E. coli (mean: 2700 cfu g(-1)) while tomatoes from Italy were free of E. coli. No helminth eggs were found in the irrigation water or on the tomatoes from Crete. Two tomato samples out of 36 from Italy were contaminated by helminth eggs (mean: 0.18 eggs g(-1)) and had been irrigated with treated wastewater and tap water, respectively. Pulsed Field Gel Electrophoresis DNA fingerprints of E. coli collected during 2008 showed no identical pattern between water and soil isolates which indicates contribution from other environmental sources with E. coli, e.g. wildlife. A quantitative microbial risk assessment (QMRA) model with Monte Carlo simulations adopted by the World Health Organization (WHO) found the use of tap water and treated wastewater to be associated with risks that exceed permissible limits as proposed by the WHO (1.0 x 10(-3) disease risk per person per year) for the accidental ingestion of irrigated soil by farmers (Crete: 0.67 pppy and Italy: 1.0 pppy). The QMRA found that the consumption of tomatoes in Italy was deemed to be safe while permissible limits were exceeded in Crete (1.0 pppy). Overall the quality of tomatoes was safe for human consumption since the disease risk found on Crete was based on only two contaminated tomato samples. It is a fundamental limitation of the WHO QMRA model that it is not based on actual pathogen numbers, but rather on numbers of E. coli converted to estimated pathogen numbers, since it is widely accepted that there is poor correlation between E. coli and viral and parasite pathogens. Our findings also stress the importance of the external environment, typically wildlife, as sources of faecal contamination. (c) 2012 Elsevier Ltd. All rights reserved.
Original languageEnglish
JournalWater Research
Issue number18
Pages (from-to)5917-5934
Number of pages18
Publication statusPublished - 2012
Externally publishedYes


  • Escherichia coli
  • Tomato
  • Treated wastewater
  • Food safety
  • Subsurface drip irrigation
  • Risk assessment
  • PFGE typing
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution
  • Ecological Modeling
  • Cropping seasons
  • Disease risks
  • DNA fingerprints
  • Domestic wastewater
  • E. coli
  • Elevated level
  • External environments
  • Faecal contamination
  • Faecal indicators
  • Fundamental limitations
  • Helminth eggs
  • Human consumption
  • Irrigated soils
  • Irrigation waters
  • Low concentrations
  • Membrane bioreactor
  • Monte Carlo Simulation
  • Parasite
  • Pulsed field gel electrophoresis
  • Quantitative microbial risk assessment
  • Solanum lycopersicum
  • Subsurface drip
  • Tap water
  • World Health Organization
  • Accidents
  • Animals
  • Contamination
  • Electrophoresis
  • Fruits
  • Health risks
  • Microfiltration
  • Monte Carlo methods
  • Pathogens
  • Soil moisture
  • Sprinkler systems (irrigation)
  • Subirrigation
  • Wastewater treatment
  • Water pollution
  • Water supply
  • Soil pollution
  • bacterial DNA
  • agricultural worker
  • bioindicator
  • bioreactor
  • drip irrigation
  • electrokinesis
  • environmental risk
  • fecal coliform
  • food safety
  • fruit
  • health risk
  • pathogen
  • risk assessment
  • sewage treatment
  • soil pollution
  • article
  • bacterium contamination
  • concentration (parameters)
  • controlled study
  • DNA fingerprinting
  • irrigation (agriculture)
  • membrane reactor
  • nonhuman
  • priority journal
  • pulsed field gel electrophoresis
  • soil
  • soil quality
  • tomato
  • waste water
  • waste water management
  • water quality
  • Agricultural Irrigation
  • Environmental Monitoring
  • Food Contamination
  • Greece
  • Lycopersicon esculentum
  • Risk Assessment
  • Soil
  • Soil Microbiology
  • Waste Disposal, Fluid
  • Waste Water
  • Water Microbiology
  • Aegean Islands
  • Crete
  • Italy
  • Bacteria (microorganisms)
  • Vermes
  • Mathematical biology and statistical methods
  • Biochemistry studies - Nucleic acids, purines and pyrimidines
  • Biophysics - Biocybernetics
  • Physiology and biochemistry of bacteria
  • Public health - Sewage disposal and sanitary measures
  • Public health - Air, water and soil pollution
  • Phytopathology - Nonparasitic diseases
  • Invertebrata: comparative, experimental morphology, physiology and pathology - General
  • Bacteria, Eubacteria, Microorganisms
  • Animals, Helminths, Invertebrates
  • Animals, Chordates, Humans, Mammals, Primates, Vertebrates
  • Angiosperms, Dicots, Plants, Spermatophytes, Vascular Plants
  • soil contamination
  • irrigation water
  • fecal contamination
  • on-site treated domestic wastewater


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