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Welcome back. In our last lesson, we spent some time discussing where our drinking
water is sourced from. The next step in our investigation is to ask: what exactly is inside our
drinking water? That will be the focus of the next two lessons.
No matter where we get it from, the water we drink every day almost always will include
small amounts of other substances. For simplicity, we can divide these substances into 4 broad
categories: physical, chemical, radiological, and biological. Physical substances are those that
change the physical properties or appearance of water. Examples include sediment or organic
material suspended in the water of lakes, rivers, and streams due to processes such as soil
erosion. Chemical substances are elements or compounds dissolved in water. These
contaminants may be naturally occurring or man-made and are often invisible to the naked eye.
Radiological substances are chemical elements with an unbalanced number of protons and
neutrons resulting in unstable atoms that can emit ionizing radiation. Biological substances are
organisms in water. They are also referred to as microbes or microbiological contaminants.
Examples of biological or microbial substances include bacteria, viruses, and protozoa. Now,
clearly, there are many types of water contaminants. But the contaminants that are causing the
most issues today are not necessarily the same ones that have caused issues in the past.
Therefore, in this lesson, we will start by learning a bit about more classic contaminants - in other words
water contaminants that have been a big problem for countries like Pakistan for quite some time now.
As always, let's begin by looking into the past. For archaeologists, understanding the
specifics of the quality of water from ancient times can be quite a challenge, since without real
samples of this ancient water, the only real way to study ancient water quality is to make
deductions from contextual factors. For example, in cities in the Indus Valley Civilization such
as Mohenjodaro, the abundance of private as opposed to public wells suggests that, at
Mohenjodaro, water purity, and pollution had become an important issue in the increasingly
congested urban setting. Also, given that water in ancient times was often accessed from
unfiltered and natural sources (such as wells or rivers), it is likely that this water still had a large
quantity of physical substances such as sediment. One source of evidence that is commonly
used to make deductions on the types of water-related diseases and water contaminants faced
by ancient peoples is through the remains and bones of ancient peoples. But, as we'll soon find
out, that's not so easy to do in climates such as Pakistan.
The site which has produced the most graves in Pakistan has been at Harappa, but even there, there are not a great many,
we maybe have 150 individuals reflected and most of these are fragmentary.
Maybe up to 100 more or less complete skeletons basically, there is some
evidence for pathological lesions and that sort of thing in these skeletons, but as far as disease
vectors are concerned, we really don't know a great deal about that. Yet, that's not saying that
it may not come because with the new developments of being able to obtain ancient DNA and
also ancient DNA of bacteria, we may actually be able to eventually get some information on
this which would be extremely interesting to know, but one could presume that these people
who lived there were basically affected by sanitation situations and by disease vectors which
existed as it happens with all populations, which happens with Pakistan today, and as a result,
but it's often hard to identify these from the skeletons because you can maybe identify a legion
or something else which happens, and but you can't really tell necessarily what precisely it
came from, the other problem is that if a person dies of a disease, the effects of that disease
may not actually show up on the skeleton at all. In other words the person is dead before it can
have changes in the skeleton which allow you to identify the disease, and that's why the
possibility of being able to get information from different parts of the skeleton would be very
nice to have but, and the big but here, South Asia is a really difficult area to get this sort of
information from, because it's hot, and it's wet, and those are two things which ancient DNA
does not like basically. In a sense that basically, it doesn't last.
Indeed, there is a lot of mystery that remains on exactly what types of diseases and
contaminants that ancient peoples in Pakistan were faced with. However, moving back into the
present day, the water contaminants relevant to modern Pakistan have been well studied.
Shallow groundwater unfortunately in those regions is heavily contaminated due to
natural geogenic sources as well as human pollution. Human pollution is typically biological and
the natural geogenic contamination is typically arsenic.
Arsenic. We will begin by talking about a chemical which increasingly has been
impacting Pakistan's groundwater supplies, but is still often misunderstood. First, what is
Arsenic? Arsenic is a solid substance naturally occurring in the Earth's crust and in crushed rock.
Normally, arsenic is located deep underground, far away from our usual sources of water.
Nonetheless, it is quite typical for small amounts of arsenic to be in regular drinking water. The
WHO has established a level of 10 micrograms per liter as the permissible concentration in
drinking water. In Pakistan, the government says that 50 micrograms per liter is acceptable. So
the question is: why are we being exposed to more Arsenic?
Actually the reason why they are exposed to it is because there were major efforts to give people access to drinking water so there were a lot of drillings
that happened and the problem was that these drillings went pretty deep, so they access parts of the
water body and the ground that wasn't previously accessed, and that had naturally very high
concentrations of arsenic, so yeah, that's why arsenic became
a huge problem and is still a big ongoing problem.
Indeed, countries in South Asia such as Pakistan have been pumping enormous
volumes of groundwater, causing the water tables to drop drastically and tapping into new water
pockets of groundwater that have been tainted by the colorless, odorless toxin. Some 50
million people are at risk of arsenic poisoning from contaminated groundwater in Pakistan's
Indus Valley. Take a look at this map. Regions in red show areas in Pakistan in which the
probability of unsafe arsenic contamination is most significant. Long-term exposure to arsenic
from drinking-water and food can cause cancer and skin lesions. It has also been associated
with cardiovascular disease and diabetes. In utero and early childhood, exposure has been
linked to negative impacts on cognitive development and increased deaths in young adults.
Thankfully, with increasing amount of research being conducted in Pakistan on water and
sanitation, government and private initiatives of finding ways to deal with this issue continue to
grow. With Arsenic covered, let's move on to another major water contaminant in Pakistan: pesticides.
Well I mean pesticides are definitely huge, a big problem coming from agriculture,
because they are highly toxic, and they have been detected in drinking water all over the world.
As we learned last lesson, agriculture is one of Pakistan's largest industries. Agricultural
compounds like fertilizers and pesticides in the farming process often mix with the irrigation
water which leach through the soil and reach water reservoirs.
Especially when it comes to farming you can imagine when you're on farmland and you use the
groundwater and you have agriculture, you use pesticides, and all these things, there's a risk
also there of being exposed to these compounds
Pesticides often come in different forms and chemical compositions, but let's look at a
specific example of a pesticide found in groundwater and drinking water across Pakistan: DDT.
DDT stands for Dichlorodiphenyltrichloroethane. It is an organochlorine insecticide that was first
synthesized in 1874. Organochlorines are often used in protecting cotton plants against insects
in Pakistan. However, since new research has uncovered the hazardous health effects of DDT
and other organochlorines, their use in Pakistan has declined. In large quantities, people
exposed to DDT report a prickling sensation of the mouth, nausea, dizziness, confusion, and
headaches, among other symptoms. Variable concentrations (0.017–1.06 μg/mL) of DDT were
detected in surface water and groundwater of different districts of Punjab, Pakistan. In
Mianchannu, district Khanewal, the concentration of DDT (1.06 μg/mL) was 10 times more than
the maximum admissible limits set by the European standards. 0.07–0.40 μg/mL of DDT in and
around a former DDT-producing factory in Aman Gharh, Nowshera was also reported. Thus,
DDT and other pesticides used in the agriculture sector in Pakistan
pose real risks to human health as water contaminants.
Finally, let's take some time to discuss biological contaminants. Biological contaminants
are organisms in water. They are also referred to as microbes or microbiological contaminants.
These biological contaminants come in a variety of species and types,
but for this lesson, we will focus on some of the key categories.
So, if we look at the microbial contamination that might be present in water, there are 3 large categories of these microorganisms
that are of concern. They include the parasites, the bacteria, and the viruses.
So these 3 groups each have their own unique characteristics, and there's 2 important
things to consider when you look at these different groups of microorganisms. The first is their
size, because size is important for transport through water, particularly and potentially ground
water, size is also important in filtration of drinking water through a conventional drinking
water treatment plant for example, so size is important, and the next most important thing is
also how long do these microorganisms stay or persist in the environment, and how easy are
they degraded by standard chemicals that are used such as chlorine
So if we put these in categories, the protozoa are the largest of the groups of
microorganisms, these include Giardia, which is worldwide, and it's about 10 microns in size, it's
a little bit larger than a red blood cell. The next protozoa of concern is Cryptosporidium, it's
smaller, about 3 microns in size, both giardia and cryptosporidium and other protozoa are very
resistant as well. They're large so they can be removed by filtration, but they're very
persistent, they can last months in the environment and still be infectious, and it takes a lot of
disinfectant to inactivate these microorganisms, and actually Cryptosporidium is not inactivated
at all by chlorine at the doses that are used for drinking water.
The next group are the bacteria, these are the ones that most people have heard about,
these include E Coli, Salmonella, Campylobacter, Cholera, Vibrio cholerae for example,
the bacteria are intermittent in size, they are about 0.5-2 microns in size, so they're smaller than the protozoa,
but they're what we call intermittent in size, and these vegetative bacteria, these labile bacteria
are actually very susceptible to degradation by chemical inactivation so chlorine can inactivate these
microorganisms quite effectively. It does not mean they're not a health concern, but they don't
persist in the environment as long as the protozoa. And the third group are the viruses, now the
viruses are very small, they're orders of magnitude smaller than the bacteria, or protozoa, and
some of the most common viruses are norovirus, it is worldwide in circulation, it is actually the
leading cause of gastroenteritis in the world now, so norovirus is one that might be in the
water. Rotavirus is another one that can be problematic, as well as Hepatitis A virus and
Hepatitis E virus in certain regions of the world. Now the viruses are very small, and they're
also quite resistant to chemical inactivation and persistence. So they're not as tough as the
protozoa, but they're much more resistant than the vegetative bacteria that, the salmonella the
campylobacter the E Coli's and the cholera. So you have these 3 groups of microorganisms each
with a different size and each with a different ability to persist in the environment or be
resistant to treatment, so if you were only going to treat water focusing on bacteria for
example, you might be able to remove the bacteria with an adequate dose a disinfectant such
as chlorine, but there might still be viruses and protozoa in that water that can be of health concern.
So to sum up, the three main categories of biological contaminants in water are parasites, bacteria, and
viruses. Now let's investigate how these organisms contaminate drinking water in the first place.
So there's different sources of the microorganisms that might be present in the water, and
obviously humans that excrete microorganisms that can cause infection in other humans are of
the biggest concern. So these are microorganisms that replicate in a human host, that are shed
by the fecal route, so in our feces, and that can get into our environment and into the water
and then an individual that consumes water that is contaminant with human waste has the
potential to become infected because its from a human source. The ones that are most
relevant here are the human noroviruses, they are shed only by humans and they cause illness
in other humans. Importantly, many groups of microorganisms, particularly the protozoa and
bacteria can come from animals. This is called zoonotic transmission, from animals to humans,
so a cow or a swine can excrete bacteria that can also cause infection in humans, so that you
can have agricultural impacts into your water environment that can cause human health
concern. So humans excreting human waste is of significant concern if an individual is sick and
excreting, others can get sick, but the animals in the surrounding
environment also of concern, we need to address that as well.
Water contamination, including biological water contamination, during ancient times is a subject
still open to scholarly debate and inquiry. However, it is safe to say that fecal contamination was
likely a danger to the ancient peoples of Pakistan as it is to modern day Pakistan. As
mentioned, one of the main causes of water contamination with harmful living organisms is
through the direct or indirect disposal of biological wastes into sources of drinking water. While
there are many ways biological wastes such as fecal matter can enter into water, let's look at a
couple of key examples in modern Pakistan for some perspective. In Pakistan, South Asia, and
much of the developing world, open defecation is one of the key factors influencing high levels
of biological contamination in drinking water. Open defecation refers to the practice whereby
people go out in fields, bushes, forests, open bodies of water, or other open spaces rather than
using the toilet to defecate. When people engage in open defecation, fecal matter has the
potential of directly mixing with reservoirs used as sources for drinking water, such as rivers,
and without proper treatment of drinking water sources, the remnants of the fecal matter and the
living organisms inside it have the potential to remain in these water sources. In Pakistan, it is
estimated that approximately 11.5% of the population practices open defecation, and while this
rate is still relatively less than some of Pakistan's neighbours (such as India and Nepal, where
the open defecation rate is closer to 50%), this practice
still poses a major water and sanitation challenge for Pakistan.
Unless the behavioral changes are brought in, there's not a clean solution to this problem.
So, let's take a look back at what we've covered in this lesson. Our focus today was in
addressing the question: What is inside our drinking water? Specifically, we learned about more
classic water contaminants. We began by first defining the 4 broad categories of substances in
water: physical, chemical, radiological and biological. We learned that there still is a lot of
mystery around the types of water contaminants impacting people in ancient Pakistan, mainly
due to limited amounts of preserved evidence. We then examined two key water contaminants:
arsenic, and pesticides. Afterwards, we spent some time discussing biological contaminants,
specifically parasites, bacteria, and viruses. In our discussion, we learned about some of the
sources of these biological contaminants, including the issue of open defecation. So let's think
back at what we've learned all together. We now have a rough understanding of where our
water comes from and some of the substances in it, specifically the more classic contaminants
that have impacted Pakistani water supplies throughout its history and today. In the next
lesson, we'll learn a little bit more about the new set of contaminants facing Pakistani water
supplies: the emerging contaminants. See you then.
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