Contaminarea încrucișată este periculoasă.

Because Romanian often puts the definite article at the end of the noun instead of using a separate word like the.

• contaminare = contamination
• contaminarea = the contamination

So contaminarea încrucișată literally means the cross-contamination.

In Romanian, this definite form is often used when talking about a concept in a general way, so even if English says just Cross-contamination is dangerous, Romanian naturally says Contaminarea încrucișată este periculoasă.

Because in Romanian, adjectives often come after the noun.

• contaminarea = the contamination
• încrucișată = cross / crossed

So the Romanian order is:

• contaminarea încrucișată
  literally: the contamination cross

This is normal Romanian word order. English usually puts adjectives before the noun, but Romanian usually puts them after.

Because adjectives in Romanian must agree with the noun in gender and number.

contaminarea is:

• feminine
• singular
• definite

So the adjective also has to be feminine singular:

• masculine singular: încrucișat
• feminine singular: încrucișată

That is why we get contaminarea încrucișată.

For the same reason: adjective agreement.

The subject contaminarea încrucișată is feminine singular, so the adjective describing it must also be feminine singular.

• masculine singular: periculos = dangerous
• feminine singular: periculoasă = dangerous

So:

• Contaminarea încrucișată este periculoasă.
• literally: The cross-contamination is dangerous.

Here încrucișată means cross- in the sense of cross-contamination.

It comes from a word related to crossed/intersecting, but in this context the natural translation is cross-contamination, not something like crossed contamination.

So:

• contaminare încrucișată = cross-contamination

This is a standard Romanian expression, especially in food safety and hygiene contexts.

In this sentence, este is the present tense of a fi (to be) and it is normally required.

• este = is

So:

• Contaminarea încrucișată este periculoasă.
• Cross-contamination is dangerous.

Unlike in some languages, Romanian generally does not omit the verb to be in normal present-tense statements like this.

It usually expresses a general truth.

Even though contaminarea is formally definite (the contamination), Romanian often uses the definite form when speaking about something in a general, class-level way.

So this sentence is best understood as:

• Cross-contamination is dangerous.

not necessarily:

• That specific cross-contamination is dangerous.

Context could make it specific, but by itself it sounds like a general statement.

Yes, but it changes the grammar and the feel of the phrase.

• contaminare încrucișată = cross-contamination as an indefinite/basic noun phrase
• contaminarea încrucișată = the cross-contamination

In a full sentence expressing a general truth, Romanian strongly prefers:

• Contaminarea încrucișată este periculoasă.

Using just Contaminare încrucișată este periculoasă would sound unnatural or incomplete in standard Romanian.

A rough pronunciation guide is:

kohn-tah-mee-NA-re-a een-kroo-shee-SAH-tuh ES-te peh-ree-koo-LOA-suh

A few useful sound notes:

• ă is a short neutral vowel, like the a in sofa
• î / â is a close central vowel, a sound English does not really have
• ș is sh
• ț is ts

So:

• încrucișată has ș = sh
• periculoasă ends with -să, where ă is that short neutral vowel

The base forms are:

• contaminare = contamination
• încrucișat / încrucișată = crossed, cross-
• a fi = to be
• periculos / periculoasă = dangerous

The actual sentence uses inflected forms:

• contaminarea = contaminare
  • definite article
• încrucișată = feminine singular form
• este = third person singular of a fi
• periculoasă = feminine singular form

You would need to change both the noun phrase and the adjective so they agree in the plural.

For example:

• Contaminările încrucișate sunt periculoase.
• Cross-contaminations are dangerous.

Changes:

• contaminarea → contaminările = the contaminations
• încrucișată → încrucișate
• este → sunt
• periculoasă → periculoase

This shows how much agreement matters in Romanian.