[newnej]

how is the synthesis of ester harmful to the environment?

[Arkcon]

We can work together to figure this one out.  How are esters made?  What do you get besides ester? These are general chemistry concepts that you can look up to start to solve the problem.  You'll also have to wonder, and then find out, how many tonnes of esters are produced, and see how companies dispose of their waste.  Now, responsible chemical companies don't release, so I don't know exactly what the issue is.  But we can try to predict possibilities.

Now, I hope you don't mind my answering your question with more questions.  That's how things are done here.  This isn't a homework finishing service.  As September approaches, I find that I have to remind people of that. We try to help you learn things for yourself, so you're better off at the end of it all.

[newnej]

The reactants of esterification process are alcohol and carboxylic acid. So you meant that the possible harmful effects during the synthesis of ester to the environment is caused by the disposal of these reactants and also the catalyst (concentrated sulphuric acid)? I heard that some esters are harmful to the environment but i do not know how.

[Arkcon]

See now, right away, you have over-simplified the problem.  Look at this page here:  http://en.wikipedia.org/wiki/Ester#Preparation  There at least six, possibly twelve methods listed right there.  And the one you mentioned, the first one has variations that don't use sulfuric acid.  So you can't say that is the problem.  Then you say, some esters are bad for the environment.  But an ester is just a carbonyl and an ether next to each other.  That page mentions that typical fats are esters -- they have to be, otherwise they can't be metabolized by typical life forms.  So I don't know where you got this assignment, or to what logical conclusion you intend to take your initial statements.