Question

Researchers in City X recently discovered low levels of several pharmaceutical drugs in public drinking water supplies. However, the researchers argued that the drugs in the water were not a significant public health hazard. They pointed out that the drug levels were so low that they could only be detected with the most recent technology, which suggested that the drugs may have already been present in the drinking water for decades, even though they have never had any discernible health effects.

Which of the following, if true, would most strengthen the researchers’ reasoning?

Option A
Option B
Option C
Option D
Option E

(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. The question can be accessed at GMAT Club)

Solution

The Story

Researchers in City X recently discovered low levels of several pharmaceutical drugs in public drinking water supplies.

Low levels of drugs were recently discovered in water supplies.

However, the researchers argued that the drugs in the water were not a significant public health hazard.

‘However’ signifies the author will present a contrast. The researchers claim that the drugs are not a significant health hazard. Why is the word ‘however’ used? To explain that although pharmaceutical drugs were found in water, the drugs are not a significant health hazard.

They pointed out that the drug levels were so low that they could only be detected with the most recent technology,

only recent technology enabled them to discover the drugs.

which suggested that the drugs may have already been present in the drinking water for decades, even though they have never had any discernible health effects.

The fact that the drugs could only be detected using the latest technology indicates that the drugs may have been present in the water for many years. Yet, there haven’t been any related health concerns in that time.

Gist: Drugs have been found in water. Since the technology to detect is new, the drugs may have been present in water for many years. Since there haven’t been any identifiable health effects, drugs in the water are not a significant health hazard (researchers’ conclusion).

The Gap

The argument is based on mere possibilities. Because we could not test for these levels of drugs in water earlier, drugs may have been present for decades. Well sure, drugs may have been present. But they very well may not have been present too. Just on the basis of this possibility the researchers build their argument and claim that the levels of drugs in water do not constitute a significant health hazard. What if the drug levels went up only recently?

Also, even if drugs have been present in water for decades, no ‘discernible health effects’ does not necessarily mean ‘no effects’. It just means effects were not identified.

There could, of course, be more gaps as well.

The Goal

We need to strengthen our belief in the researchers’ argument that the drugs in the water are not a significant health hazard. Bridging one of the gaps could be a good way to strengthen.

The Evaluation

(A) Incorrect. We need to pay close attention here. We discussed above that no ‘discernible health effects’ does not necessarily mean no health effects. If we are not precise, this option seems to alleviate that concern. However, this option actually reverses the conditional. We are interested in figuring out: if a drug found in water is a health hazard, then will its presence in the water have any discernible health effects?

Basically, on the basis of ‘no discernible health effects’ is it safe to infer ‘no high levels of drugs in water’ and thus ‘not a significant health hazard’? That is how the argument is built. The argument assumes that ‘no discernible health effects’ is sufficient to conclude ‘no significant health hazards’.

What we are given here is: ‘not a significant health hazard’ implies ‘no discernible health effects’. This option changes the direction of the sufficiency. That does not help the argument. 

Here’s an example to understand this further:

Argument: If a person does not have a blue eye, we can conclude that the person has not been in a fight. (relate this with the argument)

Statement: If a person has not been in a fight, the person cannot have a blue eye. (relate this with this option)

Does the above statement strengthen the above argument? 

Nope. Just because ~X (no fight) means ~Y (no blue eye) doesn’t mean that ~Y means ~X. We can easily have ~Y (no blue eye) and X (a fight).A person could have been in a fight with someone much weaker and not got hurt at all. He could have been hurt in other ways. He could have very well still fought. 

The same reasoning applies to this option as well.

How about this statement: If a drug found in drinking water is not a significant public health hazard, then its presence in the water will not have any discernible health effects.

What impact does this statement have on the argument?

(B) Incorrect. Researchers’ argument is that the drugs in the water are not a significant health hazard. Whether we need to remove the drugs from water is beyond their argument. 

(C) IncorrectScientists may not have discerned ‘which’ adverse health effects a health hazard has caused. This is not the same as scientists may not have discerned ‘whether’ there were adverse health effects. Even if the scientists were not able to pinpoint which adverse health effect a substance caused they could have still understood ‘whether’ a substance had adverse health effects.

Let us also consider the statement we made above: Scientists may not have discerned (detected) whether there were adverse health effects. Does this statement strengthen the argument? It doesn’t. It actually weakens the argument. This is the second gap we have discussed above.

(D) CorrectSo researchers did detect these drugs in the water in another town decades ago. And they could not find any visible side effects. Ok, so these drugs very well may be present in the water and yet there may not be any noticeable effects. That does increase our belief in the researchers’ reasoning. These drugs do not manifest any noticeable health effects, and likely are not a significant public health hazard.

Let’s look at one more aspect. How come researchers were able to detect the drugs ‘several decades ago’ when the passage states that ‘they could only be detected with the most recent technology’? The passage says that the levels were ‘so low’ that only the latest technology could detect the drugs. So, if in a neighboring town researchers could detect the drugs several decades ago with older, less sensitive technology, that indicates that the levels of drugs would have been higher. If even those higher levels did not lead to any discernible health effects, it is likely that even the current low levels would not and thus the drugs in the water are not a significant health hazard.

(E) IncorrectWait a minute. Old samples did not have the drugs? That would likely mean that the reason there were no ‘discernible health effects’ is that there were no drugs in the water. The drugs perhaps only recently got added to the water. This option is clearly in the opposite direction, and weakens the argument.

Before we get too engrossed in the nitty-gritty, it helps to understand what ‘direction’ an option is taking our argument in. This one clearly is going in the opposite direction. It reduces our belief in the reasoning and is thus incorrect.

Additional Notes

SC Notes

  1. In the third statement of the passage, notice the use of ‘which’ to refer to the entire clause.  
  2. Notice the three occurrences of ‘they’ in the third statement. 

They (researchers – mentioned in the previous sentence) pointed out that the drug levels were so low that they (drugs – mentioned in the previous sentence) could only be detected with the most recent technology, which suggested that the drugs may have already been present in the drinking water for decades, even though they (drugs) have never had any discernible health effects.

This solution was created by Anish Passi and Chiranjeev Singh.

If you have any doubts regarding any part of this solution, please feel free to ask in the comments section.

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