"The conditions are the same for everyone; we've got no excuse. We just weren't there," Froome, who was attempting to become the first man in 24 years to win the Tour and world road race in the same year, told BBC Sport.
"It's a big disappointment, especially having made it such a big objective, but with these conditions it just wasn't meant to be.
"The first three laps on the circuit, there were crashes everywhere. It's rained solidly all day. After three laps the split started happening and I looked around and realised I didn't have any team-mates left and it wasn't going to happen.
"Given we've come up empty-handed, we'll have to go back to the drawing board [ahead of the Rio Olympics in 2016]."
Route for 2013 men's road race
San Baronto (5km, max gradient 13%)
10x 16.57km circuits around Florence
San Domenico (4.3km, max gradient 9%) and Via Salviati (600m, max gradient 16%)
Froome's withdrawal meant Geraint Thomas was the only Briton left riding, but he also pulled out shortly after.
"It was just carnage out there," Thomas told BBC Sport. "I saw five or six crashes out in front of me.
"Once you're in that back half, you're kind of destined to get dropped. We all committed to try and get Froome there, but it wasn't meant to be."
2011 world champion,
led the peloton and helped keep Britain in contention for much of the first 106km after the race left Lucca.
However, as soon as the race hit the first of 10 laps around Florence, featuring two significant climbs, the Italian squad took over the pace-setting and Cavendish fell away.
Wiggins, who had been expected to support Froome in the latter stages of the race, was always near the back of the peloton and soon retired along with Cavendish.
The punishing 16.5km circuits, coupled with the horrendous weather conditions, were taking their toll with riders dropping out at an average of around 15 a lap.
Poland's Bartosz Huzarski, who broke away with four other riders early in the race, held on to the lead for around 240km.
He was finally caught with a little over 25km remaining, by a group of 40 riders that included
defending champion Philippe Gilbert
and fellow pre-race favourites Peter Sagan of Slovakia and Switzerland's Fabian Cancellara.
However, the trio were unable to respond when Italy's Michele Scarponi, Rodriguez and Nibali attacked on the final 4.3km climb to Fiesole , eventually finishing in a group 34 seconds behind Costa.
Recent world champions
Philippe Gilbert (Bel)
Mark Cavendish (GB)
Thor Hushovd (Nor)
Cadel Evans (Aus)
Alessandro Ballan (Ita)
Rodriguez rode away from
Giro d'Italia champion Nibali,
who had crashed on an earlier descent, but was unable to open a significant advantage on the final ascent of the 600m-long Via Salviati.
Costa broke clear of Nibali and Valverde to catch Rodriguez with one kilometre remaining, before making the decisive move in a laboured sprint to become the first Portuguese world champion.
"Losing like this is stupid," said a tearful Rodriguez. "Winning is all that matters so this medal doesn't mean anything to me right now.
"We (Spain) had the numbers; we were the strongest; we should not have lost."
Also in the British team were Ian Stannard, Josh Edmondson, Steve Cummings and Luke Rowe, who replaced Jonathan Tiernan-Locke.
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