When I read one text about 'River pollution' there was one sentence and I couldn't find what this is referring to.

The biofilms are able to break down the pesticides that contaminate aquatic environments and modify their structure, diversity and functioning. Toxic substances, for example can change the photosynthetic, enzymatic, respiratory activity of aquatic ecosystems, either definitely or temporarily. It is in this way biofilms can serve as an early warning signal of pollution.

What is the sentence in bold referring to?

...It remains to characterize and distinguish the responses of biofilms to pollutants from those induced by environmental factors (current speed, physio-chemical composition, etc.).

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    Biofilms can serve as an early warning signal in this way - that is, in the way described in the previous two sentences. Commented Dec 21, 2022 at 10:07
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    It's a badly written paragraph. It's not at all clear how biofilms can be a signal. There's no method even suggested since it doesn't describe how biofilms or their work breaking things down are detected, and the second sentence is a non-sequitur since toxic substances changing activity is not an example of biofilm activity, as presumably the biofilms would break down the toxic substances before they were able to change activity in the ecosystem.
    – gotube
    Commented Dec 21, 2022 at 17:44
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    Please provide proper attribution for the text that you quote. That means title, author, and publication, or as many of those as are available. If the source is long, such as a book, please include a page number or other location also. If the source is online, please include a link also. See Marking and Attributing Examples, Sources, and Other Quotes Commented Dec 22, 2022 at 18:05
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    How is the second quote related to the fist? is it part of the same passage? Commented Dec 22, 2022 at 18:07

2 Answers 2


First of all, the boldface expression "*It is in this way *" is not a sentence, nor even a clause. It menas that biofilms can serve as a signal in the manner previously described. But neither of the previous sentences included inn the quote describes how biofilms can act as a signal of pollution. Unless this is described earlier in the passage, this is unclear writing.

Moreover, the first quoted sentence is ambiguous as to whether biofilms modify the properties of the toxins, or their own properties. Perhaps more context would clarify this, but I incline to doubt it.


As passage suggests biofilms can serve as an indicator for river pollution. By saying in this way they are referring to response of biofilms to toxic substances.

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