Sporco vs. sporcizia
While both sporco and sporcizia translate to "dirt" or "filth" in Italian, they differ slightly in usage. Sporco is often used to describe the substance of dirt itself or the state of being dirty, while sporcizia usually refers to accumulated filth, trash, or a general condition of squalor.
Sporco
A2This word is originally an adjective meaning "dirty", but it is frequently used as a noun to refer to the physical substance of dirt on a surface, skin, or clothing. Sporco focuses on the grime itself.
Devi strofinare forte per togliere lo sporco dai vestiti.
(You have to scrub hard to remove the dirt from the clothes.)
C'è dello sporco sotto le tue unghie.
(There is some dirt under your fingernails.)
Questo detersivo elimina lo sporco più ostinato.
(This detergent eliminates the most stubborn dirt.)
Ho notato un po' di sporco sulla lente della fotocamera.
(I noticed a bit of dirt on the camera lens.)
Lui puzza di sudore e di sporco.
(He smells of sweat and dirt.)
Sporcizia
B2This is a noun that refers to accumulated dirt, filth, sweepings, or litter. Sporcizia often implies a collection of dirty things, waste, or a neglected state of hygiene in a room or area.
La casa abbandonata era piena di polvere e sporcizia.
(The abandoned house was full of dust and filth.)
Non lasciare la tua sporcizia sul tavolo quando te ne vai.
(Do not leave your trash on the table when you leave.)
C'è troppa sporcizia per le strade di questo quartiere.
(There is too much filth in the streets of this neighborhood.)
Il vento ha spazzato via tutta la sporcizia dal cortile.
(The wind swept away all the filth from the courtyard.)
Dobbiamo pulire la sporcizia che si è accumulata dietro il divano.
(We need to clean the filth that has accumulated behind the sofa.)
Summary
In short, use sporco when you are talking about the actual grime or substance on a specific object or person (like a spot on a shirt). Use sporcizia when referring to piles of dirt, litter, or a general environment of mess and filth.