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Why Don’t We Use Mothballs Anymore? - Video học tiếng Anh
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Why Don’t We Use Mothballs Anymore?
Why Don’t We Use Mothballs Anymore?
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0:00
If you’ve snooped around your grandma’s attic or wound through the shelves at a vintage bookstore,
0:04
then you might be familiar with mothballs.
0:07
Or rather, their smell.
0:08
They have a sharp, overwhelmingly sweet, tar-like scent reminiscent of old tobacco smoke.
0:14
It’s a smell so distinct that I bet you’re wrinkling your nose right now.
0:18
And it’s also why we’re not opening this bag.
0:20
But that smell, and really mothballs in general, are becoming far less common.
0:24
We just don't really see—or smell—them much anymore.
0:27
For more reasons than you might think.
0:29
[♪ INTRO]
0:33
For those of you who haven’t encountered these pungent little balls before,
0:36
they’re intended use is to deter moths.
0:38
Except “moth ball” is actually a bit of a misnomer.
0:41
It’s not the moths that are the problem, it’s the larvae.
0:44
There are several species of clothes moths that can become household pests, but all species are
0:50
super into the protein-maxxing trend, and their protein of choice is fibrous keratin.
0:54
And what better place to chow down than our closets full of keratin-rich wool,
0:58
silk, fur, and leather.
1:00
They’re pretty shy about their eating habits, and by that I mean they often
1:03
hide in the protected nooks of clothes, or the backside of furniture and rugs.
1:08
Plus, the larvae are translucent when they’re first born, making them hard to spot.
1:12
So usually your first sign of an infestation would be lots of new holes in your clothes,
1:17
which happened to me a couple of months ago!
1:19
Eventually they’ll build a cocoon out of silk from their bodies as well as bits of fabric.
1:23
Then they’ll lay in wait to transform into an adult moth,
1:26
who lays eggs and the cycle starts again.
1:28
But our closets aren’t the only places that clothes moths hang out.
1:31
Keratin is also in vintage bookbinding glue and leather book covers.
1:36
Museums are also prime targets, with their massive collections of keratin-full preserved specimens.
1:41
And clothes moths are one of our most ancient nuisances.
1:44
Even Alexander the Great’s housekeeper had
1:46
to be diligent about brushing clothes to dispel the moths.
1:49
So you could say for a while now people have been pretty keen on getting rid of these critters.
1:53
In the past that mostly meant natural deterrents, like chips, chests, or hangers made from cedar.
1:59
Which, is lovely smelling, but there’s mixed evidence about whether it actually works.
2:03
Cedar fumes can kill very young larvae, but research has shown
2:07
they unfortunately aren’t effective against older larvae or adult moths.
2:11
Plus, cedar lumber eventually loses its essential oils that smell so nice to humans.
2:16
And within a few years the vapor concentrations aren’t high enough to deter even the young larvae.
2:21
Then there’s the added downside that, over time,
2:23
cedar can become acidic and leave yellow stains on the fancy clothes you’re trying to protect.
2:28
And there seems to be a bit of a smelly theme when it comes to deterring moths.
2:32
Other popular smelly options are oils like lavender, eucalyptus, rosemary or camphor,
2:37
an oil distilled from the camphor tree, a large evergreen tree native to East Asia.
2:42
You probably know what those first three smell like, but in case you’re
2:44
not familiar with camphor, it’s a sharp, nostril-opening, almost turpentine smell.
2:49
It’s an ingredient in Vicks Vaporub and Tigerbalm.
2:52
Although to be fair those both have a bunch
2:54
of additional smelly compounds as well, like menthol and eucalyptus.
2:58
All of these are quite different scents but one thing they have in common,
3:01
chemically speaking, is that they contain terpenoid compounds — organic molecules
3:05
made from links of a 5-carbon structure called isoprene.
3:09
Terpenoids are pretty common in a lot of plants,
3:11
and they seem to disrupt the nervous and digestive systems of some moth
3:15
larvae… but unfortunately don’t protect against the moths that eat your clothes.
3:19
A recent study at least found that, as a gas,
3:22
camphor does deter red ants by disrupting their climbing and feeding behavior.
3:27
But again.
3:28
No moths.
3:28
So after many years of a battle against the bugs with smelly substances of… questionable substance,
3:34
you can imagine how satisfying it must have felt to finally discover
3:37
something that was proveably effective against those wool-munching nuisances.
3:41
Enter mothballs.
3:43
Which we’ll talk about in detail right after this quick break.
3:47
Since you watch SciShow, you probably like engaging with
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4:32
In 1948 chemists standardized the production of a white crystalline,
4:36
volatile solid chemical called naphthalene aka the main ingredient in mothballs.
4:41
This was a long time coming though, since naphthalene was first discovered
4:45
all the way back in 1819 by a Scottish chemist when he was distilling coal tar.
4:50
Which is actually not too different from how naphthalene is made today.
4:54
Some 90% of naphthalene is made by burning coal tar at super high temperatures and cracking
5:00
the chains of molecules apart into the fused pair of benzene rings we know as naphthalene.
5:06
It’s also made during natural combustion processes like burning wood or tobacco.
5:10
Chemists later created a more effective compound
5:12
called paradichlorobenzene.And this one was kind of by accident!
5:16
While making explosives for the First World War,
5:19
chemists noticed they’d made a strong-smelling byproduct.
5:22
They passed it along to entomologists, who then made it into an insecticide.
5:26
Paradichlorobenzene also has a benzene component,
5:29
as the name suggests, except this compound is synthesized by adding chlorine gas.
5:34
Again, as the name kind of suggests.
5:37
And as its history suggests,
5:38
this clever little compound can be used in a couple of different ways.
5:42
Anyone who’s spent time around urinals might recognize the smell
5:45
of paradichlorobenzene because it’s the main compound in urinal cakes.
5:49
If you’re not familiar with the smell,
5:51
you can pause the video and take a trip to your nearest public bathroom and learn for yourself.
5:58
As well as bathrooms, you might find it in your closet or under
6:00
the kitchen sink as an odor eliminator block.
6:03
Its deodorizing ability means it also shows up in cleaning products,
6:06
leaving you with that super clean smell.
6:08
But it’s also a potent fungicide that helps control plant diseases.
6:12
And it’s an insecticide against not just our little moth foes but also silverfish.
6:17
But what is it about naphthalene and paradichlorobenzene,
6:20
over cedar or camphor, that make them so effective?
6:23
If you’ve been following along, you might have noticed a theme here: Smell.
6:26
Part of the reason these substances are so
6:28
infamously smelly is because they have pretty low odor thresholds,
6:32
meaning we notice the smell even when only a few of the molecules make it up our nostrils.
6:36
So, that’s part of the answer.
6:38
Another is that they sublimate easily, meaning they turn straight from solid to gas.
6:43
They’re able to do that because the compounds have a high vapor pressure.
6:46
Basically the molecules of the bulk substance push against the
6:50
air more strongly than atmospheric pressure,
6:53
lowering the energy barrier for molecules to peel off the solid and change states to a gas.
6:59
It’s that gas that works as a pesticide.
7:02
But maybe most importantly, those gaseous compounds don’t just deter
7:05
but can actually kill larvae and adult moths.
7:09
Now, there’s not much information on how they work, but one study on mosquitoes found that
7:13
naphthalene might interrupt the functioning of the larva’s respiratory organ, or siphon.
7:18
Trouble is, they may be too good at their job.
7:21
Naphthalene and paradichlorobenzene have turned
7:24
out to be almost as bad for humans as they are for bugs.
7:27
We started to understand the health risks through good ol’ toxicity
7:31
testing on animals but also several case studies where people, especially children,
7:36
had accidentally eaten a mothball or two.
7:39
Because of those cases some countries, like New Zealand, don’t allow them at all,
7:43
since there’s too much of a risk of children being poisoned by eating them.
7:47
And it’s not just children.
7:48
There have been cases of adults ingesting them too.
7:50
Whichever way you come into contact with naphthalene from mothballs,
7:53
its effect is pretty similar.
7:55
In the body, naphthalene is broken down into alpha-naphthol and then other compounds,
7:59
which can interfere with enzymes or damage cells.
8:02
Red blood cells explode, known as hemolysis, which can lead to anemia.
8:07
It also damages the lining of your lungs and mucus membranes.
8:10
At first that looks like inflammation, but after a while they can kind of end
8:14
up permanently swollen – at least in mouse studies.
8:17
If that’s not enough, naphthalene is also carcinogenic.
8:21
Paradichlorobenzene is a little less toxic, causing eye or throat irritation when it’s first
8:26
inhaled, but also ultimately ends up damaging your blood cells, liver, kidneys, and sometimes
8:32
central nervous system, leading to weakness, slow reflexes, trembling or slurred speech.
8:37
And even camphor, although it seems more natural,
8:40
can irritate the esophagus, stomach, and liver if it's eaten.
8:43
It can also lead to vertigo, confusion, delirium, seizures and coma in young children.
8:48
Remember, natural does not always mean safer!
8:51
By the late 1990’s it had become pretty clear, through experiments and formal
8:55
toxicology reviews by agencies like the Environmental Protection Agency in the US,
8:59
that naphthalene was bad news for our health and not worth a few sweaters.
9:04
Which meant mothballs started coming with some stern warning labels.
9:08
They’re still available as pesticides,
9:10
but there’s also plenty of other things we can do to help keep moths at bay.
9:14
For example, cleaning your clothes in hot water and then storing them in an
9:17
airtight container is usually enough to make that woolen sweater unappetizing.
9:21
Larvae will actually seek out soiled patches on clean garments, so the cleaner the better.
9:26
It also helps to bring that sweater out every month and give it a little shake.
9:30
Clothes moths love that chill life and hate being disturbed.
9:32
The same goes for carpets.
9:34
Regularly vacuuming and cleaning them gets rid
9:36
of the lint and animal hair that larvae love to feed on.
9:39
And walking on those carpets also helps disrupt the moths.
9:42
If there is an infestation, there are other, less toxic ways to deal with it,
9:47
like pheromone traps or water-based insecticides.
9:50
Or, just put the clothes in the freezer for two weeks inside a sealed bag! Easy!
9:54
But those fuzzy sweaters and cozy carpets may not even need that much saving anymore.
9:59
Not only are mothballs a thing of the past, but so, to some extent, are moth infestations.
10:04
Climate control keeps our homes relatively cool and dry, where bugs like things warm and wet.
10:09
Plus it means we keep our windows and doors closed,
10:11
so less chance of moths getting in in the first place.
10:14
The few places clothes moths might still be a problem is in more humid regions
10:18
or in older houses with lots of lovely crevices for moths to creep in through.
10:23
But just like our homes have changed, our clothes have changed too.
10:26
It’s far more likely to see rayon or polyester
10:29
printed on the tag than it is to see 100% pure wool.
10:32
Even a lot of animal fibers these days are blended
10:35
with other stuff to get the stretch or softness benefits of synthetic fibers.
10:39
Which is good, in this case at least, since moth larvae just
10:42
can’t digest synthetic fibers or even some plant-based proteins like cotton or linen.
10:47
So that distinct mothball smell might be on its way out.
10:50
Although maybe you’ll still catch a whiff if someone wearing a vintage
10:53
coat stands behind you while in line at the flea market.
10:56
Clothes moths no longer plague us the way they did for centuries because we’ve changed the moth’s
11:00
environment through heating, the way we wear clothes, and what those clothes are made of.
11:05
We’ve narrowed their niche, so now holey sweaters are nearly a thing of the past.
11:10
[♪ OUTRO]
