Often, submitted samples are divided and one portion retained as a reference in case the original sample is lost, or a further date required. Sometimes, submitters perform basic pretreatments, usually involving a wash in distilled water and the removal of root material. This should be reported in the submission forms accompanying samples sent to the laboratory. Contamination Contamination may be artificially or naturally caused. Artificial contamination may be blamed on human negligence during the collection and processing of samples.
Natural contamination occurs in the post-depositional environment.
Samples may be contaminated by material which make any radiocarbon result either too old or too young. The most common source of contamination by modern carbon is caused by rootlet intrusion. Contamination may also be caused by humic acids circulating throughout the soil. Humics are the decayed remnants of dead plants. They may exchange carbon or adhere to samples that have large surface areas and make any radiocarbon results too young.