9. Chemical Hazards ( WHO：Lead )
10. Lead in Drinking-water ( WHO Guidelines )
2.2 Water ( see P.2 )
With the decline
in atmospheric emissions of lead since the introduction of legislation restricting
its use in fuels, water has assumed new importance as the largest controllable
source of lead exposure in the USA (10).
Lead is present in
tap water to some extent as a result of its dissolution from natural sources,
but primarily from household plumbing systems in which the pipes, solder,
fittings or service connections to homes contain lead. Polyvinyl chloride (PVC)
pipes also contain lead compounds that can be leached from them and result in
high lead concentrations in drinking-water. The amount of lead dissolved from
the plumbing system depends on several factors, including the presence of
chloride and dissolved oxygen, pH, temperature, water softness and standing
time of the water, soft, acidic water being the most plumbosolvent (11,12).
Although lead can be leached from lead piping indefinitely, it appears that the
leaching of lead from soldered joints and brass taps decreases with time (10).
Soldered connections in recently built homes fitted with copper piping can
release enough lead (210–390 µg/l) to cause intoxication in children (13). The
level of lead in drinking-water may be reduced by corrosion control measures
such as the addition of lime and the adjustment of the pH in the distribution
system from <7 to 8-9 (14, 15). Lead can also be released from flaking lead
carbonate deposits on lead pipe and from iron sediment from old galvanized
plumbing that has accumulated lead from lead sources such as plumbing and
service connections, even when the water is no longer plumbosolvent.
In 1988, it was
estimated that a lead level of 5 µg/l was exceeded in only 1.1% of public water
distribution systems in the USA (16). A more recent review of lead levels in
drinking-water in the USA found the geometric mean to be 2.8 µg/l (10). The
median level of lead in drinking-water samples collected in five Canadian
cities was 2.0 µg/l (17). A recent study in Ontario (Canada) found that the
average concentration of lead in water actually consumed over a 1-week sampling
period was in the range 1.1–30.7 µg/l, with a median level of 4.8 µg/l (18). In
the United Kingdom in 1975– 1976, there was virtually no lead in the
drinking-water in two thirds of households, but levels were above 50 µg/l in
10% of homes in England and 33% in Scotland (2). In Glasgow (Scotland), where
the water was known to be plumbosolvent, the lead concentration in about 40% of
the samples exceeded 100 µg/l (19).
If a concentration
of 5 µg/l in drinking-water is assumed, the total intake of lead from this
source can be calculated to range from 3.8 µg/day for an infant to 10 µg/day
for an adult.
2.5 Estimated total exposure and relative
contribution of drinking-water ( see P.3 )
More than 80% of
the daily intake of lead is derived from the ingestion of food, dirt and dust.
At 5 µg/l, the average daily intake of lead from water forms a relatively small
proportion of the total daily intake for children and adults, but a significant
one for bottle-fed infants. Such estimates have a wide margin of error, as it
is not known to what extent the general public flushes the system before using
tap water; in addition, the stagnation time (and hence the lead levels) is
highly variable (10). The contribution of ingested dust and dirt to the total
intake is known to vary with age, peaking around 2 years (32).
( see P.14 ) There remain uncertainties
associated with the epidemiology, which relate to very low blood lead levels
and end-points that are affected by many factors. Nevertheless, because lead
exposure arises from a range of sources, of which water is frequently a minor
one, and as it is extremely difficult to achieve a concentration lower than 10
µg/l by central conditioning, such as phosphate dosing, the guideline value is
maintained at 10 µg/l but is designated as provisional on the basis of
treatment performance and analytical achievability.
11. Home Lead Poisoning
Lead-contaminated
drinking water is
most often a problem in homes that are either very old or very new. Up through
the early 1900s, it was common practice to use lead pipes for interior
plumbing. Also lead piping was often used for the service connections that join
residences to public water supplies. Copper pipes have replaced lead pipes in
most residential plumbing. However, the use of lead solder with copper pipes is
widespread. Experts regard this lead solder as the major cause of lead
contamination of household water in U.S. homes today. Lead concentrations in
drinking water can be also be elevated if your home has faucets or fittings of
brass which contains some lead. The most common cause of lead getting into
drinking water is corrosion, a reaction between the water and the lead pipes or
lead solder. Lead can leach into the water from the joints or from lead pipes.
Dissolved oxygen, low pH (acidity), and low mineral content in water are common
causes of corrosion. One factor that increases corrosion is the practice of
grounding electrical equipment, such as telephones, to water pipes. Any
electric current traveling through the ground wire will accelerate the
corrosion of lead in the pipes. Most well and city water does not usually
contain lead. Water can pick up lead inside the home from household plumbing
that is made with lead materials. The only way to know if there is lead in
drinking water is to have it tested. Contact the local health department or the
water supplier to find out how to get the water tested.
New brass faucets
and fittings can also leach lead, even though they are "lead-free".
Scientific data indicate that the newer the home, the greater the risk of lead
contamination. Lead concentrations decrease as a building ages. This is because,
as time passes, mineral deposits form a coating on the inside of the pipes (if
the water is not corrosive). This coating insulates the water from the solder.
But, during the first five years, before the coating forms, water is in direct
contact with the lead. More likely than not, water in buildings less than five
years old has high concentrations of lead contamination.
12. NSF61, NSF372 and Lead
13. Explaining NSF61 and NSF372 for Plumbing Systems
The “Reduction of Lead in Drinking Water Act” was enacted
on January 4, 2011 and signed by President Obama. The purpose of this Act was
to amend Section 1417 of the Safe Drinking Water Act (“SDWA” or “the Act”). The
Act established a prospective effective date of January 4, 2014, which provided
a three-year time frame for affected parties to transition to the new requirements.
Since 1986, the Safe Drinking Water Act has prohibited
the use of certain items that are not lead free and since 1996 the Act has made
it unlawful for anyone to introduce into commerce items that are not lead free.
The primary purpose of the 2011 change was to lower the maximum lead content of
the wetted surfaces of plumbing products such as pipes, pipe fittings, plumbing
fittings and fixtures from 8.0% to a weighted average of 0.25%. The Act also
established a statutory method for the calculation of lead content (now known
as Annex G). Finally, to eliminate the requirement that lead free products be
in compliance with voluntary standards established in accordance with SDWA
1417(e) for leaching of lead from new plumbing fittings and fixtures. Since the
voluntary standard was eliminated, this made it clear to the industry that the
lead content requirements would now be mandated, which would require
“Third-Party Certification” by a “Nationally Recognized Testing Laboratory”.
14. Lead in Plumbing ( Safe Plumbing Organization )
It is essential to the nation's health
that lead piping systems be upgraded, a task estimated by the EPA in 2003 to
cost $276.8 billion and take more than 20 years achieve. In the meantime, the
best protection for the U.S. public is the ongoing testing and monitoring of
what makes up our drinking water.
The EPA allows faucets to be sold in the U.S. that do not
leach more than 11 parts per billion of the lead into water during a 19-day
test. That is comparable to a teaspoon of water in an Olympic-sized pool. The
EPA's criteria is in accordance with the Safe Drinking Water Act (SDWA), taking into account the extremes of potable water
chemistry that interact with the pipes and faucets across the U.S. Contrary to
some erroneous claims, faucets do not increase the amount of minerals that are
leached over time. In fact, the amount decreases over time.
15. Lead in Drinking Water ( NSF：The Public Health and Safety Organization )
16. 科學理性看待「鉛水」問題
http://paper.wenweipo.com/2015/07/23/WW1507230001.htm
其他資料
Body Mass Index Diagram
Obesity
Introduction
The
Body Mass Index (BMI) is one of the methods for measuring overweight
and obesity. It is calculated by dividing the body weight (in kg) by
the square of height (in m): kg/m2. For Chinese adults living in Hong
Kong, BMI from 23.0 to less than 25.0 kg/m2 is classified as
overweight and BMI 25.0 kg/m2 or above is classified as obese.
Obesity
increases the risk for a number of chronic diseases, such
as hypertension, heart diseases, hypercholesterolaemia,
diabetes mellitus, cerebrovascular disease,
gall bladder disease, osteoarthritis, sleep apnoea and some types of
cancer (breast, prostate, colorectal and endometrial).
Situation
in Hong Kong
The
Behavioural Risk Factor Survey April 2014 revealed that 39.0% of the
population aged 18 - 64 were classified as overweight or obese (BMI ≥
23.0), including 20.8% as obese. A higher proportion of males (49.6%)
than females (29.5%) were classified as overweight or obese. People
aged 45 - 54 had a highest rate (50.5%) of overweight or obesity.
