Sure you are not thinking of Modified Vegetable Oils or Straight Vegetable Oils? When you have treated the veggie oil to get "Biodiesel" as opposed to MVO or SVO, what is the fuel you end up with? A Methyl-Alkyl Ester compound.

When developing common rail fuel pumps RME (bio-diesel with up to 15% rape seed oil derived methyl esters) is one of the fuels used for accelerated wear tests as it has a much lower lubricity than ordinary Diesel.

In fact this fuel and the more extreme winter fuels (which are virtually kerosene) give premature high pressure fuel pump failure. This problem is exacerbated at high fuel temperatures.

Viscosity and thus lubricity decreases dramatically with temperature leading to scuffing of internal components. A pump seizure can also wreck your engine by preventing the camshaft from rotating, thus snapping your cambelt.

For anything with a modern CDi engine, avoid Methyl Ester biodiesel like the plague unless you are certain that it contains sufficient lubricity additives or just add a few quarts of SVO or MVO. The Bosch CP1 pump as found in CDi models until fairly recently failed frequently in Germany with their readily available Bio-diesel. So much so that DaimlerChrysler insisted on special tests for new pumps.

Rudolph Diesel's engines did not run at 4000 rpm plus, and with injection pressures of 23200 psi. These are the major engineering challenges for Diesel Fuel Injection equipment manufacturers and the bio diesel lobby both of whom obviously want to push "green fuels" but have been a bit coy about the fact that it is not all good news with modern high pressures diesels.

These fuels are not a problem for heavy duty engines as their pumps can be much bigger, and there is space to have an engine oil lubrication system for the pump. Older diesels or those with lower pressure systems do not suffer as they are not so critical of the lubricity quality of the fuel, but if they have rubber or other non synthetic seals you can get problems.

As for the toxicity of biodiesel, a commonly quoted factoid is that biodiesel has tested "less toxic" than table salt so it is non toxic. Hmmm. Does not take a lot of salt to kill you: try drinking seawater.