Is there any harm in throwing(trashing) small objects on the ground? I mean like tissue a size of a coin, or some dirt, or other things which seems to not cause harm if trashed improperly

All perfect praise be to Allah, The Lord of the Worlds. I testify that none is worthy of worship except Allah and that Muhammad is His slave and messenger.

A Muslim is required, as per the Sharee‘ah, to maintain cleanliness in general and the cleanliness of the streets in particular. He must not dispose of garbage except in the designated waste containers, because the Islamic Sharee‘ah preaches cleanliness and urges Muslims to remove harmful objects from the roads. The Prophet said: “Whoever removes a harmful object from the pathways of Muslims, Allah will write a good deed for him; and anyone for whom Allah has written a good deed, He will admit him into Paradise by virtue of it.” [Al-Albaani: Hasan in Saheeh Al-Jaami‘]

In the same vein, Al-Mawsoo‘ah Al-Fiqhiyyah reads: “It is recommended to remove objects that are harmful to Muslims wherever they are found. The Prophet considered the removal of harmful objects from the road an aspect of faith. He said: ‘Eemaan (faith) has seventy odd branches; the uppermost of which is [the Testimony of Faith] 'La ilaaha illa Allah' (testifying that none is truly worthy of worship but Allah), while the least of them is the removal of a harmful object from the road.’” [End of quote]

We do not know of any Sharee‘ah evidence indicating the prohibition of throwing the like of what you mentioned in the street, as long as throwing it does not cause harm to others. As for harmful objects, like glass and similar things, that are likely to harm some people, it is incumbent to refrain from throwing them in the street to avoid harming people. This is evidenced by the general indication of the statement of the Prophet : “There should be neither harm nor reciprocal harm.” [Ahmad and Ibn Maajah; Al-Albaani: authentic]

Allah Knows best.