Using transport biofuels may change the emissions of non-greenhouse gases, if com­pared with the original (fossil) fuel. For instance, the substitution of fossil diesel by biodiesel (fatty acid ester) reduces sulphur dioxide emissions but tends to increase the emissions of nitrogen oxides (NOx) from diesel, whereas the acute effects on res­piratory organs do not change significantly (Ban-Weiss et al. 2007; Lin et al. 2007; Swanson et al. 2007; Szybist et al. 2007). The increase of NOx emissions caused by switching to biodiesel can be reduced by adjusting timing of the injection pump (Kegl 2008). The impact of substituting fossil diesel by biodiesel on particulate matter emissions by motorcars is apparently complex, with evidence that biodiesel substitution impacts the nanostructure of diesel soot, enhances oxidative reactivity and cytotoxicity but reduces mutagenicity (Bunger et al. 2000; Szybist et al. 2007). It appears that the overall amount of particulate matter and the number of particles that is emitted is reduced when fossil diesel is progressively replaced by biodiesel, which seems indicative of reduced risk. But the average particle size is also reduced (Kegl 2008; Keskin et al. 2008; Lapuerta et al. 2008), and smaller particle size is correlated with increased risk of a specified mass of particulate matter (Lapuerta et al. 2008). The overall effects of all these changes on human health impacts await further research (Swanson et al. 2007).

It would seem likely that, if compared with fossil gasoline, the admixture of ethanol to gasoline may be able to reduce emissions of CO and reduce ambient O3 concentrations (Ahmed 2001). On the other hand, the emission of acetaldehyde is in­creased by such a substitution, and there may also be an increase in the atmospheric concentration of peroxylacetate nitrate (PAN) (Ahmed 2001). What the overall im­pact thereof on health will be awaits further research. Moreover, in practice, ethanol (or ETBE) may not substitute fossil hydrocarbons but other oxygenates of MTBE. It would seem doubtful that, as far as its impact on inhaled air is concerned, such a substitution would benefit health (Ahmed 2001).

Changes in non-greenhouse gas emissions are not confined to cars; they concern the complete life cycles. And indeed, a substantial part of the seed-to-wheel non­greenhouse gas emissions is, for instance, associated with the cropping stage. This stage is associated with the input of fertilizers (‘nutrients’) and pesticides. Nutrients (including conversion products thereof) may be emitted into the wider environment. Well known is the leaching of P and N nutrients into water. Leaching of these nu­trients from arable soils in the US Midwest, where corn is grown to supply ethanol, is a primary contributor to the hypoxic zone in the Gulf of Mexico (Powers 2007). Hypoxic zones due to elevated levels of nutrients also occur in the East China Sea and several continental European seas, whereas continental shelves of Africa, South America and India are relatively vulnerable to increases in nutrient emissions (Diaz and Rosenberg 2008). More in general elevated concentrations of nutrients may lead to eutrophication. Eutrophication is linked with harmful algal blooms and reduced biodiversity (Graneli and Turner 2006; Ptacnik et al. 2008).

Even the cropping of Jatropha, which produces nuts with well-known insectici­dal properties, may require substantial pesticide inputs to reduce the impact of pests (Grimm 1999; Grimm and Somarriba 1999; Carvalho et al. 2008). More generally, cropping is also associated with the use of pesticides, which may lead to ecotoxicity and toxic effects on humans. In some cases, handling of harvested materials may have a large impact on non-greenhouse gas emissions. A case in point is the burning of harvest residues of sugar cane, which serves as feedstock for the production of bioethanol. This has an adverse impact on populations living in areas where sugar cane is harvested, especially on the respiratory systems of children and the elderly (Cangado et al. 2006).

The most comprehensive study regarding transport biofuel life cycles is the work of Zah et al. (2007), who compared traditional fossil fuels with a variety of plant-based biofuels, such as rapeseed methylester, palm oil methylester, soybean methylester, methanol and ethanol from various biomass sources and countries of origin, regarding seed-to-wheel non-greenhouse gas emissions. Allocation was on the basis of prices. Zah et al. (2007) considered the life cycle emissions that may lead to oxidizing smog, eutrophication and ecotoxicity. In many cases, the emis­sion of ecotoxic substances was found by Zah et al. (2007) to be lower for crop — based transport biofuels than for fossil fuels. However, there were also exceptions. Biodiesel from Malaysian palm oil and Brazilian soybean oil gave rise to seed-to — wheel emissions that were at least five times more ecotoxic than the fossil petrol or diesel life cycle emissions. As to eutrophication, plant-based biofuels tended to do worse than fossil transport fuels over their respective life cycles, with the exception of some wood — and grass-based products that scored rather similar to fossil trans­port fuels. Regarding the emission of hydrocarbons which may lead to oxidizing or photochemical smog, biofuels did often somewhat better than fossil fuels. How­ever, soybean-based biodiesel, Malaysian oil-palm-based biodiesel and bioethanol from sugar cane in Brazil did much worse regarding their seed-to-wheel emissions of compounds that may cause oxidizing smog.

Zah et al. (2007) did not consider acidifying substances (NO*, SO2, NH3, HCl), but other studies suggest that in this respect, biofuels often do worse than fossil fu­els (Kaltschmitt et al. 1997; Sheehan et al. 2003; Reinhardt et al. 2006; Kim and Dale 2008a), when allocation is on the basis of prices. Reinhardt et al. (2006) con­sidered a variety of processes that convert lignocellulosic biomass into transport fuels via synthesis gas. Apart from the life cycle emissions of acidifying substances, they looked at plant nutrients and compounds that may be toxic to humans, while allocating on the basis of prices, and concluded that such transport lignocellulosic biofuels did in these respects mostly worse than fossil fuels. When allocation would have been on the basis of energy content or weight of output, the emissions allo­cated to transport biofuels would have been lower than in the case of allocation on the basis of prices. Kim and Dale (2008a) looked at ethanol derived from US corn grain by dry milling and found that this did worse than conventional gaso­line as to eutrophication and photochemical smog. In this case, allocation was done by substitution. Graebig (2006) has considered the relative environmental impacts of electricity from photovoltaics and from biogas generated by the conversion of maize. It was concluded that photovoltaics were better in all life cycle assessment categories, except eutrophication.

Zah et al. (2007) also studied waste-to-wheel emissions associated with methane production from a variety of wastes and compared these with natural gas. They found that the emission of hydrocarbons, which contribute to oxidizing smog asso­ciated with methane from wastes, was somewhat larger, and the emission of eutro —

phying substances much larger than in the case of natural gas. Emissions of ecotoxic substances were roughly similar or somewhat larger. The outcomes of the study of Zah et al. (2007) seem more favourable to transport biofuels made from wastes than to transport biofuels made from food crops. However, one should keep in mind that this verdict is based on the assumption that life cycle impacts up to the waste can be neglected. When wastes change into secondary resources, fetching a price, or when the allocation in life cycle assessment is based on mass or energy, differences between transport biofuels made from, for example, starch and from residues would become smaller.