JasonC wrote:
Hi, I know a local creek a few kilometres away. It is REALLY murky. So should I take care when going to get samples? What precautions should I take. And how should take my samples?
JasonC 13 Of Western Sydney
Science is what we know as "Something".
Toby Fiander replied:
Some Precautions for Sampling in a Creek Rubber gloves are a good idea. If you have no others some from the kitchen will do, but they are hard to work in. A better idea would be to get some disposable rubber gloves from the Supermarket. They come in big packets and are not very expensive. Put the gloves on before you leave the car and take them off just before you get into it. You should also wear a glove on the hand that you use to control the sample when you get it back to have a look at it.
Incidentally, creeks are along drainage lines and these are favourite places to find the rubbish that people throw away. Mostly this is pretty harmless, but it is possible to find used syringes, broken glass, sharp metal objects and a range of other things that may injure you. The general rules are:
... never put your hands in a place you cannot see, ... move slowly (unless there is some other danger you are escaping I suppose), ... don't work alone, ... take enough tools with you to do what you have to do so you are not tempted to use your hands directly instead; and if you don't have the right tool with you, go and get one, ... keep your wits about you, pay attention to what you are doing and try to anticipate what you are going to have to do next. ... don't touch your nose, mouth or eyes when you have your gloves on; have a good wash in soap when you get home and THEN you can scratch your nose.
How to Sample Water (typical only) It sounds silly, doesn't it....
To sample your water you need to make sure your bottle is clean. If you are using a PET bottle that has been used for softdrink, then wash it out in warm water several times before you put it in the car to go to the creek to sample. Put the lid on tightly when you are finished washing. If you are sampling for bacteria you should disinfect your bottle and if you are sampling for heavy metals you need to acid-wash your bottle, but assuming you are doing none of these things, just make sure it is nice and clean (including the threads of the lid) and put the lid back on.
When you get to the site near the creek, put your gloves on a pick up the bottles to take with you. If you have a few, get a bag or a bucket to put them in so you can carry them without dropping them everywhere when you are coming back up the hill.
Find a spot where the water of the type you wish to sample and deep enough to get your sample bottle into the water. If you stand just on the bank so you do not get wet, then you will have to crouch down and stay that way while for quite a while, so make yourself comfortable. Open your bottle and place it under the water so you do not disturb the sediment on the bottom or the floating material on top - this is never easy to do and most sampling locations are a bit of a compromise. When the bottle is about a quarter full, take it out, put the cap on and wash the bottle out in the liquid. Discard the liquid away from you. If you are sampling on land, discard it behind you, but preferably so you do not get wet. You need to wash the bottle out three times in the liquid you are sampling.
Now you are ready to take your sample. You might need to use a smaller dipper to fill the bottle if you are having trouble getting enough water without stirring up the bottom or the material floating on the surface. If you are taking a sample where oxygen is going to be important, make sure you exclude air-bubbles from the bottle by filling it full and squeezing it slightly as you put the lid on.
Finally, when you have your sample, make sure you keep it in a safe place at about the temperature or a bit cooler than the sample was when you got it. If you are sampling a biological process, then the time between when you sample and when someone measures it needs to be minimised and in the mean time, the sample needs to be preserved, usually this means cooling in a foam cooler with an ice-brick.
Sounds elaborate for what is really a fundamentally simple operation, but my experience is that reliable water sampling looks simple, but hardly ever is and if anything is going to go wrong with your results it will be in the sampling.
BTW, if you have no idea what sort of water you are dealing with, you should consider all the possible things that can have happened to it before you arrived to sample it and treat it with the respect it deserves.
Toby
PS. During the writing of this, it
has been pointed out to me that I actually don't always use rubber gloves
myself. Of course, that is not the recommended way of doing things.
I figure that I know not to touch my nose, mouth and eyes until I have
had a good wash in antiseptic soap and water, but then I have had my shots
for Hepatitis-B as well and you won't have done that yet. So... I
think on a first time out sampling in an urban creek, or even a rural creek,
you ought to have rubber gloves - get some of the good disposal kind from
a (larger) Supermarket and keep them on hand for the other experiments
you are going to do on the next few years.
