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Impact of Marine Environmental Pollution on Human Health

We may be dealing with a global problem with major economic implications in the multi-billion dollar range every year

Society generally views recreation at the seashore and ocean bathing as a positive experience for health.

However, there has been some degree of historical awareness of the potential human health problems associated with bathing and harvesting shellfish – which are often eaten raw – in marine coastal waters contaminated by urban wastewater discharges.

In the past these health risks have been perceived primarily as isolated local problems. The issue of marine biotoxin poisonings associated primarily with toxic algae blooms has also been of concern.

However, the dramatic global impact of these human health problems has recently been underscored by a new study aimed at developing a preliminary quantitative estimate of the impact of these pathways of disease transmission. This has been underscored by other recent studies.

Any comparison of health impacts from various sources must start with a sense of scale of the health problems. Which health impact is more important in human disease and social terms or in financial terms, and by how much?

In [one 1999] preliminary study [Shuval, H. (1999). The impact of microbial pollution in the marine environment on human health. A preliminary quantitative estimate of global disease burden (GDB). 24 pp, unpublished document of the GESAMP Working Group on Marine Environmental Assessments], each of these negative health impacts has been evaluated in terms of the concept of Global Disease Burden – GDB. The GDB is measured in units of Disability-Adjusted Life Years – DALYs, a new concept recently developed by the World Health Organisation (WHO) and the World Bank [see World Development Report, 1993].

This new approach calculates

i) losses from premature death, defined as the difference between the actual age of death and life expectancy at that age in a low-mortality population, and

ii) years of loss of healthy life resulting from disability.

It is difficult to estimate the social and economic loss of one year of productive life resulting from premature death or disability (or one “DALY”). There are numerous approaches for making such economic estimates. For the purposes of this study, Shuval’s study, in consultation with the WHO, […] estimated the money value of the economic loss of one productive year of life, or one DALY, as being US$4,000. This figure approximates the global mean annual GDP per capita, but it is not necessarily based on that figure.

Infectious Diseases Related to Bathing/ Swimming in Marine Coastal Waters Contaminated by Wastewater Discharge

There is massive epidemiological evidence that enteric and respiratory diseases can be caused by bathing/swimming at marine coastal beaches contaminated with pathogenic micro-organisms, i.e., exposure to pollution from domestic wastewater sources.

The evidence from 22 highly credible epidemiological studies clearly supports the conclusion that the rate of infections and disease among bathers increases steadily with increasing concentrations of indicator micro-organisms of fecal pollution in a dose-response relationship.

These studies also support the conclusion that bathers face the risk of enteric and respiratory infection and disease even in lightly polluted coastal waters meeting current microbial standards of the European Union and US EPA.

Based on an extensive and careful evaluation of the available credible epidemiological evidence, WHO [in 1998] estimated that bathing in what had previously been considered “acceptable” marine waters with a mean concentration of 50 faecal streptococci/100 ml will result in infection and illness in 5% of the adult bathers after a single marine bathing exposure.

In Shuval’s study slightly higher risk-of-disease rates were used for children (who are more susceptible than adults), for adults visiting beach resorts in countries with high endemic disease rates, and for a certain percentage of highly contaminated beaches.

Working from official reports from the World Tourism Organisation and estimates from other sources, [the 1999] study calculated that some 1-2 billion marine-exposure-days are spent at beach resorts each year by local residents and foreign tourists. From these global figures – and the WHO risk estimates for gastroenteritis and respiratory infections at various levels of beach pollution [–] a highly tentative estimate has been made that some 250 million clinical cases of mild gastroenteritis and upper respiratory disease are caused every year by bathing in contaminated seawater.

Why has this situation gone unnoticed and unreported for so long? Epidemiological studies have revealed that minor cases of gastroenteritis are rarely seen by medical care professionals and even less frequently reported to health authorities. The ratio of actual clinical cases to reported cases of mild gastroenteritis can be 1000:1.

Calculated in terms of DALYs the number of cases results in some 400 thousand DALY units. The economic impact or financial loss resulting from this amount of disease has been estimated at some US$1.6 billion/year.

Infectious Diseases Related to the Consumption of Seafood Harvested in Marine Coastal Waters Contaminated by Wastewater Discharge

Seafood – and particularly molluscs normally eaten un-cooked – is a commonly implicated vehicle for the transmission of infectious diseases caused by enteric micro-organisms (including bacteria and viruses) that enter the marine environment through the disposal of urban/domestic wastewater.

Pathogenic bacteria can remain viable in the sea for days to weeks, and viruses can survive in the marine environment or in the tissues of fish and seafood for months. Filter-feeding shellfish – whose breeding areas are often placed near sources of nutrients, such as wastewater outfalls or polluted estuaries – are highly prone to concentrating high levels of pathogens.

A series of studies involving testing for and detecting viruses in shellfish in the United States found enteric viruses in 19% of 58 pooled samples taken from waters meeting current US bacteriological standards for shellfish growing and harvesting.

A mean virus concentration in the shellfish meat of 10 PFU (plaque forming units) per 100 grams of shellfish meat was observed [according to a 1993 report]. One unpublished survey of enteric viruses in shell-fish in a Paris market in 1978 indicated that 25% were contaminated with pathogenic enteroviruses.

Infectious hepatitis A (HAV), a most serious and debilitating disease of the liver, is the gravest virus disease very frequently transmitted by shellfish.

Conventional depuration techniques are used to help clean shellfish harvested in contaminated waters. Shellfish are held in clean, disinfected water tanks for 36-48 hours of self cleansing.

This is partially effective in removing bacterial contamination, but less effective for viruses, which are tightly adsorbed to the internal tissues of the molluscs.

Thus, eating raw or lightly steamed shellfish harvested from such contaminated – but considered acceptable – marine waters can cause infection and disease in a significant percent of the exposed population.

There is firm epidemiological evidence for numerous sporadic cases – not reported as part of epidemics – of the transmission of infectious hepatitis (IH) by eating raw or lightly steamed shellfish. In [a 1967 study] it was reported that some 25% of all the cases of IH during a non-epidemic period in Boston were apparently associated with the ingestion of raw or lightly steamed shellfish. Similar figures were found in England [according to a 1991 study].

Rose and Sobsey (1993) have written the seminal work on the development of the methodology for quantitative risk assessment associated with exposure to virus contamination in shellfish [Rose J.B., and M.D. Sobsey (1993), "Quantitative risk as-sessment for viral contamination of shellfish and coastal waters", Journal of Food Protection, 56, 1043-1050].

They have estimated that the risk of infection for infectious hepatitis virus A for individuals who consume one raw shellfish serving of 60 grams harvested from approved waters in the United States is about 1 per 100, or 1%.

The risk from highly polluted waters is greater.

Based on reports from the FAO, it has been estimated that some 8 million tons of molluscs, including clams, oysters, mussels and cockles, are harvested and marketed globally each year. Assuming that one kilogram of gross shellfish, including shells, is required for each shellfish meal or serving, Shuval (1999) has estimated that some 8 billion shellfish meals are consumed globally per year.

Working with the assumption that some 88-90% come from clean safe waters and/or are not eaten raw, and using the risk of infection and disease drawn from the risk estimate study of Rose and Sobsey (1993), Shuval (1999) has estimated that each year there are about 2.5 million clinical cases of infectious hepatitus globally, with some 25,000 fatalities and 25,000 cases of long term disabilities from liver damage caused by eating contaminated shellfish.

This level of disease results in some 1.8 million DALYs with an estimated economic impact of US$7.2 billion per year.

Diseases Associated with Contamination of Shellfish and other Seafood with Toxins from Toxic Algae Blooms

Marine biotoxins cause a large number of poisonings in humans annually, many with serious sequelae and causing frequent fatalities.

Most of these poisonings are in the subtropical/tropical circumglobal belt region bounded by Florida, the Mediterranean and Japan in the north and the northern edge of Australia, the southern tip of Africa and Chile in the South.

The human diseases most frequently associated with marine biotoxins are amnesic shellfish poisoning (ASP), paralytic shellfish poisoning (PSP), ciguatera poisoning, and the more recently identified neurotoxic shellfish poisoning (NSP) and diarrhoeic shellfish poisoning (DSP).

Most of these diseases are apparently associated with fish and seafood that feed on toxic marine algae and toxic algae blooms such as red tides. PSP in particular can lead to severe neurotoxic effects, paralysis and death.

The death rate for PSP and some of the other marine biotoxin diseases appears to be in the range of 10%-20% or higher: serious long-term sequelae, such as neurotoxic effects and paralysis, are common. There have been numerous local reports of outbreaks, and of high endemic incidence, of ciguatera poisoning in small communities and islands in the Pacific, such as Tahiti, Hawaii, Samoa and New Guinea, where the incidence has been estimated to be about 500 per 100,000 population.

A similar incidence was reported in Dade County, Florida [in a 1988 study]. [A 1983 study] estimated that 10,000-50,000 individuals are afflicted worldwide each year by ciguatera poisoning alone. [The 1988 study] estimates that the true rate of ciguatera poisonings for the South Pacific is likely to be 2,500 per 100,000.

The case fatality rate is low (about 0.1%). It is estimated that the total population in the circumglobal belt where the disease is endemic is about 400 million people, 10% of whom live near sea-coasts and frequently eat locally caught fish and seafood.

If the incidence rate of ciguatera poisonings is 500/100,000, then the global incidence might be 200,000 cases a year. If the rate is 2500/100,000 as estimated [in the 1988 study], then the global incidence might be 1,000,000 a year. In the latter situation, a case fatality rate of 0.1% would result in 1,000 fatalities per year.

In Canada, which has one of the best marine biotoxin monitoring and control programs, there are an estimated 1000 cases per year of illness caused by seafood toxins, with 150 cases per year of PSP and 350 cases of ciguatera poisoning.

If the incidence for Canada – of about 3.3 cases/100,000 for all marine biotoxin poisonings per year – is representative of the temperate zones globally, then it might be possible to extrapolate a minimum global incidence for the world population of some 6 billion persons at about 200,000 cases per year, with some tens of thousand fatalities and tens of thousand cases with serious life long sequelae.

This would be a minimum since the rate for the tropical belt, where these diseases are highly endemic, would be expected to be much higher.

In light of the above very scanty data on global incidence of disease from marine biotoxins , Shuval (1999) was only able to make a very rough first approximation of the GDB.

He estimated that marine biotoxins associated primarily with toxic algae blooms cause some 100,000 to 200,000 serious cases of poisoning a year globally, some 10,000 to 20,000 deaths and a similar number of cases with very serious neurological sequelae, such as paralysis.

More accurate or reliable global information is not available at this time. Shuval’s crude first estimate of the GDB and the DALYs based on the above was that it might be as high as one million DALYs per year, with an estimated global economic impact of some four billion US dollars.

Global Impact of these Human Health Effects

The total estimated impact of the illnesses associated with land-based marine pollution may be about 3.2 million DALYs/year, with an estimated economic loss of some US$ 13 billion dollars per year[…]

The loss of life years and their associated economic loss is very significant, with the impact being similar to that from up-per respiratory tract infections and intestinal nematodes.

Shuval (1999) has pointed out that the estimates above are at best only rough first approximations which must be taken with reservations and used with caution. They may serve as a basis for determining a rough order of magnitude of the global scope of the problem, which appears to be very much larger than previously estimated. The very provisional economic evaluation of this impact of marine pollution must be viewed with caution, since it is based on a very preliminary and unconventional economic approach. However, it might suggest that we are dealing with a global problem with major economic implications in the multi-billion dollar range every year.