The phrase "are sometimes contaminated" is correct and usable in written English.
It can be used when discussing the occasional presence of impurities or unwanted substances in a particular context, such as food, water, or products.
Example: "The samples collected from the river are sometimes contaminated with harmful bacteria, posing a risk to public health."
Alternatives: "may occasionally be tainted" or "can sometimes be polluted."
Specialists here say Chinese fish farmers often turn to illegal veterinary drugs because they can help keep fish alive in overcrowded ponds that are sometimes contaminated by sewage, agricultural runoff and industrial chemicals.
DNA specimens, for instance, are sometimes contaminated; fingerprint, ballistics and even run-of-the-mill drug and alcohol analyses depend on human interpretation and thus are subject to error.
The echo signals less than 100 km are sometimes contaminated by the clutter or meteor and the F region beyond 800 km signals often become unusable owing to the weak signal strength.
It should be noted that the occurrence of keratin K9 (and K1 and K10) may give rise to problems in biochemical practice as biochemicals or buffers are sometimes contaminated with these keratins derived from abraded "horny particles", i.e. terminally differentiated skin keratinocytes ("laboratory dust"; Clark et al. 1971; Fox et al. 2008).
For a few hours, he suffered as does much of the rest of Baghdad, where electricity lasts for but a few hours, water is sometimes contaminated, trash piles up in the streets and the infrastructure is crumbling.
One employee, John C. Karjanis, who from 1996 until 1998 was manager of product evaluation for the company, the Mentor Corporation, said some top executives instructed him to destroy reports detailing the high rupture rates and poor quality of some types of implants because the products "are in the customers". He also said the implants were sometimes contaminated with fleas.
BabyGanics' "naturally derived plant-based cleaning agents" include sodium laureth sulfate, they told me, which is sometimes contaminated with 1,4-dioxane, a well-established carcinogen.
But in mid-2013 loose-fill asbestos was again found in a house, and it became clear the original program had in many cases not successfully removed the fibres, which remained in the walls and was sometimes contaminating living areas through cracks or openings.
The widespread use of the weapons also overwhelmed Iran's poorly trained and equipped medical personnel, who were themselves sometimes contaminated during rescue efforts.
The risk of infection with intestinal parasites to the population is increased because these contaminated vegetables are sometimes eaten raw, undercooked to retain the natural taste and preserve heat-labile nutrients, or unclean [ 22].
Hunters who handle wild game in the field are sometimes unaware of the risk of contaminating the meat with foodborne pathogens while dressing, handling, and transporting it.
