WGK (Wassergefaehrdungsklassen)
The German Water hazard classes

English Document

Pure plant oils are the only renewable engine fuels of today which are completely harmless to the environment, especially the groundwater.

According to the VwVwS (Verwaltungsvorschrift wassergefaehrdende Stoffe), which is the national German regulation on water hazard classification, all substances are either classified as non-hazardous to water (nwg, nicht wassergefaehrdende) or assigned to one of three classes, WGK 1, WGK 2, and WGK 3, with increasing water hazard.

Pure plant oils such as rape seed oil, are classified as non-hazardous to water (nwg).

The other two currently used renewable engine fuels, biodiesel and ethanol, are both classified in WGK 1, whereas fossil diesel and gasoline are classified in WGK 2 and WGK 3 respectively.

In comparison to WGK 3 and WGK 2, the lowest class WGK 1 may seem relatively harmless and close to non-hazardous (nwg), but as it appears from VwVwS, it only takes a mass share of 3% WGK 1 to make a mixture hazardous to water (section 2.2.2a in VwVwS).

Also, it should be noted that one argument for the harmlessness of biodiesel, namely that only a small part of the methanol is present in the final product, is not very convincing from an environmental point of view, because biodiesel and methanol are classified alike in WGK 1, which also includes the byproduct glycerine. In other words: the esterification of the pure plant oil to produce biodiesel changes a harmless product into a water hazardous main product and a water hazardous byproduct.

The following list with German names and index numbers may illustrate which types of substances share WGK 1 with biodiesel and ethanol:

Acetone (Aceton: 6)
Laughing gas (Lachgas: 767)
Carbon monoxide (Kohlenstoffmonoxid: 257)
Copper oxide (Kupferoxid: 1401)
Glycerine (Glycerin: 116)
Methanol (Methanol: 145)
Silicone A and B (Silikone A, B: 542, 543)

A number of acids, including:

Acetic acid > 25% (Essigsaeure: 93)
Boric acid (Borsaeure: 315)
Butyric acid (Buttersaeure: 41)
Nicotinic acid (Nicotinsaeure: 1368)
Oxalic acid (Oxalsaeure: 166)
Perchloric acid (Perchlorsaeure: 390)
Phosphonic acid (Phosphonsaeure: 1269)
Phosphoric acid (Phosphorsaeure: 392)
Propionic acid (Propionsaeure: 483)

A number of salts, including chlorides, nitrates, and sulphates, of:

To find the relevant engine fuels or other substances, either read the annexes or search (at present only possible in the German version). Examples:

Search for:

Rapsöl = rape seed oil = Index number 760,
Rapsoelmethylester = biodiesel = Index number 834,
Ethanol = ethanol = Index number 96,
Dieseloel = diesel = Index number 76,
Benzin = gasoline = Index number 204

Source:
The German ministery for environmental protection (Umweltsbundesamt):
http://www.umweltbundesamt.de/wgs-e/wgs-index.htm