4: The increasing global mercury threat
industrialization over the last two centuries has increased
levels of mercury in the environment. Although a naturally
occurring metal, excess mercury in ecosystems can be highly
toxic; it accumulates in living tissue and is particularly
associated with underdevelopment of the nervous system.
Mercury contaminates the water cycle, both directly and indirectly,
although the most significant releases of mercury are into
the air. Once deposited, mercury can change to methyl mercury
and become concentrated as it moves through the food chain
risks of mercury are more severe than was previously understood.
To address the growing mercury challenge, it is necessary
to reduce the use of mercury, substitute or eliminate mercury-containing
products and processes, control its emissions with end-of-pipe
technologies, and manage mercury wastes.
|Source: UNEP 2003a
While industry does not use the largest
quantities of freshwater, nor produce the largest volume of water pollutants,
it is responsible for the production and use of some of the most hazardous
water pollutants (Fry and Rast 1998). These include heavy metals such
as mercury (Box 4), polychlorinated biphenyls (PCBs), industrial solvents
and other organic chemicals dangerous to environmental and human health.
Groundwater represents 90 per cent of the world’s readily-available
freshwater (Boswinkel 2000). An estimated one-and-a-half billion people,
a quarter of the world’s population, depend directly on this source
for their drinking water (Shiklomanov 1997). It is also the main source
for irrigation in many countries. Despite their importance, groundwater
resources are often overexploited, managed badly, and their dynamics
are usually poorly understood. As a result, they are under constant
threat of degradation from contamination and depletion. For example,
poor irrigation practices and drawdown of groundwater near coastal areas
can both result in groundwater salinization. Poor sewage, waste and
effluent management can result in the release of pollutants into surface
waters and allow contamination of aquifers. Depletion occurs through
overexploitation of available groundwater and land use changes that
alter surface run-off and reduce the replenishment of groundwater supplies
On a global scale, agriculture is the main source of both nitrate
and ammonia pollution of surface and groundwater (FAO 2003c; see also
the section on Emerging Challenges). In addition to damaging many aquatic
organisms or making water less suitable for drinking, excessive loading
of nutrients in river basins can result in eutrophication and algal
blooms in coastal waters, and the formation of deoxygenated (hypoxic)
zones which threaten benthic marine life and economically important
fisheries (Figure 4).
4: Hypoxia in the northern Gulf of Mexico
image of the northern Gulf of Mexico/Mississippi Delta, showing
hypoxic coastal water (light blue), January 2003
Comparative size of hypoxia areas between 1985–2002.
Nutrient enrichment is
causing dense algal blooms and a growing hypoxic area.
|Source: Jacques Descloitres, MODIS Land Rapid Response
||Source: Rabelais and others 2002
Where strong measures have been taken and sustained to reverse negative
trends some improvements in water quality have been achieved. For example,
nearly 30 years of European Union (EU) environmental legislation, with
national and international actions to protect and improve the aquatic
environment, are yielding results (EEA 2003). Pollution of rivers and
lakes by phosphorus and organic matter from industry and households
has been reduced and the pollution of rivers with heavy metals and other
hazardous substances is generally decreasing. There has been progress
in reducing overall water withdrawals and use in most parts of Europe.
There is, however, little or no progress in combating nitrate and pesticide
pollution, and water withdrawals for irrigation, energy use and tourism.
Weak data on some issues mean that the conclusions listed above must
be treated with caution (EEA 2003). Overall, there are still knowledge
gaps about the world’s freshwater quality. Better data collection
and information systems are required to provide reliable, consistent
and appropriate freshwater data and information (Box 5).
5: Water quality data
water quality data collection and monitoring systems are inadequate
data coverage (spatial and temporal);
reporting and sharing of data; and
training and capacity of local water authorities to collect
data. The main steps to invest in monitoring, assessment, and
information systems are to:
monitoring programmes in water management plans, and invest
in data collection and analysis capacity in countries, particularly
in Africa, SIDS and Central Asia;
country participation in regional and global water quality monitoring
and assessment programmes, such as GEMS/Water; and
that data and information about water quality are collected
frequently and regularly using comparable methods.
Over 800 stations for freshwater monitoring worldwide have contributed
data to the UNEP GEMS/Water Programme (see map below). Of these,
98 are measuring water quality in lakes and reservoirs. There
are four types of stations:
stations are located in areas where there is little
or no effect from point sources of pollutants and removed from
obvious anthropogenic influences;
stations are located at sites with at least one major
use of the water such as drinking water supply, irrigation,
or conservation of aquatic life; Trend stations are primarily located on large rivers that are representative
of large basins in which human activity is high; and Flux
stations are monitoring at the mouths of major rivers
upstream from estuarine effects.
By the end
of 2003, the GEMS/Water database contained more than two million
data points covering over 100 water quality parameters, including
physical/chemical parameters, such as temperature, pH, major
ions, nutrients, metals, microbiological parameters, and organics.
As the requirements for assessment and identification of national,
regional and global water quality issues of concern increase,
the need for data that accurately reflect environmental conditions
geographic distribution of the data contained in the GEMS/Water
database is widespread with a higher concentration of stations
in European countries, India and Japan.
|Source: GEMS/Water 2003