The interaction of human microbial pathogens, particulate material and nutrients in estuarine environments and their impacts on recreational and shellfish waters

Abstract

Anthropogenic activities have increased the load of faecal bacteria, pathogenic viruses and nutrients in rivers, estuaries and coastal areas through point and diffuse sources such as sewage discharges and agricultural runoff. These areas are used by humans for both commercial and recreational activities and are therefore protected by a range of European Directives. If water quality declines in these zones, significant economic losses can occur. Identifying the sources of pollution, however, is notoriously difficult due to the ephemeral nature of discharges, their diffuse source, and uncertainties associated with transport and transformation of the pollutants through the freshwater-marine interface. Further, significant interaction between nutrients, microorganisms and particulates can occur in the water column making prediction of the fate and potential infectivity of human pathogenic organisms difficult to ascertain. This interaction is most prevalent in estuarine environments due to the formation of flocs (suspended sediment) at the marine-freshwater interface. A range of physical, chemical and biological processes can induce the co-flocculation of microorganisms, organic matter and mineral particles resulting in pathogenic organisms becoming potentially protected from a range of biotic (e.g. predation) and abiotic stresses (e.g. UV, salinity). These flocs contain and retain macro- and micro- nutrients allowing the potential survival, growth and transfer of pathogenic organisms to commercially sensitive areas (e.g. beaches, shellfish harvesting waters). The flocs can either be transported directly to the coastal environment or can become deposited in the estuary forming cohesive sediments where pathogens can survive for long periods. Especially in response to storms, these sediments can be subsequently remobilised releasing pulses of potential pathogenic organisms back into the water column leading to contamination of marine waters long after the initial contamination event occurred. Further work, however, is still required to understand and predict the potential human infectivity of pathogenic organisms alongside the better design of early warning systems and surveillance measures for risk assessment purposes.

Effects of rainfalls variability and physical–chemical parameters on enteroviruses in sewage and lagoon in Yopougon, Côte d’Ivoire

“…Although flocs represent a passive substrate for viral attachment and persistence, nutrient interactions that promote flocculation would ultimately enhance virus attachment and promote survival, as virus surrogate further work is necessary on enteroviruses in the same conditions (Shapiro et al 2013;Malham et al 2014). In fact, further work is necessary to disentangle the interactions between allochthonous pathogens and estuarine nutrients, particularly with respect to the impact of enhanced nutrient deposition due to storm events, waste discharges and eutrophication.…”

“…It is now widely recognized that flocs account for approximately 80 % of the total volume of sediments in suspension within estuaries. These flocs contain and retain macro-and micronutrients allowing the potential survival, growth and transfer of pathogenic organisms to commercially sensitive areas (e.g., beaches, shellfish harvesting waters) (Malham et al 2014).…”

“…Today, these diseases are the cause of very high mortality rates in the populations of developing countries. Several studies have been conducted throughout the world to show the relationship of environmental factors on the variation of the concentration of bacterial fecal pollution indicators such as Escherichia coli, Clostridium perfringens and enterococci (Anderson et al 2005;Fries et al 2006;Melek 2012;Malham et Racyte et al 2014). The presence and levels of bacterial indicators do not always correlate with the presence and concentration of viruses, especially when these indicators are present in low concentrations.…”

Survival of Viruses in Water

“…Few authors have addressed the detection of real viruses in real environments over long periods [50]. Such results would be helpful in assessing the persistence of virus infectivity in the environment [51,52]. Interactions of viruses with other microorganisms (infection targets, protective hosts, etc.)…”

Stratification in the presence of an axial convergent front: Causes and implications

“…Dynamics taking place in an estuary determine how much pollution is delivered to the marine environment (Elsdon et al, 2009). Rivers transport enhanced nutrient loading, heavy metal concentrations, faecal bacteria and pathogenic organisms from anthropogenic activities including agriculture and sewage discharge (Malham et al, 2014). In particular, it is well known that human microbial pathogens preferentially attach to sediment and in estuarine systems, the chemical and physical properties of the sediments mean that heavy metals become easily incorporated (see Wang et al (2014) and references therein).…”