Along the malecon front in the capital the trash seems to come and go, I,m not sure why or how this occurs but one day you can walk along the malecon and you will see a sea of plastic, 2 days later walk the same length and it has vanished. I'm not convinced it all comes out of santo Domingo though as people dont tend to sit on the waters edge so wouldn't throw the trash in the sea. I think it could be a tidal thing and maybe trucks are dumping off a cliff somewhere up the coast, I dunno, I don't understand tides and all that stuff.
Rats get me going, every day on my way to work I'll find myself stepping over and occasionally in rotten fruit and waste meat dumped on the street for the binmen. It is pure laziness as often there will be a green big bin 10 Mtr away.
I remember the first time I visited la Caleta (boca) to meet some distant family. I couldn't get my head around how they had so much trash in the side of the house and in the garden, plastic bags, rotten fruit remains, disgusting, but it doesn't seem to register this will attract rats and other unwanted pests, besides being just outright filthy.
As far as dead animals on the sides of roads, in the north I noticed where ever there were dead animals they lit a car tyre and burnt it over the dog or cat, apparently gets rid of the smell.
In bavaro very recently the Haitian workers working on s nearby block killed an old horse, they butchered what was eatable and dumped the rest in the gutter on the other side of the road from us, the smell was terrible for about 2 weeks.
Common sense just doesn't exist among many.