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Despite the increasing agricultural use of biochar as a way of combining the utilization of biomass for energy production with the removal of CO(2) from the atmosphere, it is not known how variations in pyrolysis temperature and feedstock type affect concentration and composition of polycyclic aromatic hydrocarbons (PAHs) that inevitably form and associate with biochar. To close this knowledge gap, we quantified 11 unsubstituted three- to five-ring PAHs as well as alkylated forms of phenanthrene and anthracene in grass and wood chars produced in 100 °C increments across a temperature range (100 to 700 °C). Our results show that solvent-extractable PAH concentrations in biochars produced at heat treatment temperatures (HTTs) of 400 and 500 °C greatly exceed those observed at higher and lower temperature, supporting a low HTT solid-phase formation mechanism operable at temperatures commonly used for industrial biochar production. The maximum extractable yield of 'pyrolytic' unsubstituted PAHs for grass (22 μg g(-1) at HTT = 500 °C) greatly exceeds the value for wood (5.9 μg g(-1)). Moreover, PAH signatures (e.g., total monomethylphenanthrene to phenanthrene ratios, MP/P ~2-3) at intermediate temperatures (400 °C) resemble those of fossil oils rather than that commonly attributed to pyrolytic products. Further research is needed to characterize the PAH evolution in modern pyrolysis reactors and assess the fate of biochar-bound PAHs in soils and sediments. Various commonly applied PAH ratios and indicator compounds show promise as markers for specific feedstock materials and pyrolysis conditions of biochars in environmental systems.

[1] We conducted isothermal (15°C) batch culture experiments with the coccolithophorid Emiliania huxleyi (strain NEPCC 55a) to evaluate the extent to which nutrient and light stress contribute to variability in the alkenone unsaturation index U 37 K 0. Alkenone content and composition were constant throughout exponential growth in both experiments when nutrients (nitrate and orthophosphate) were replete. Stationary phase (nutrientstarved) cells continued to produce alkenones, amassing concentrations (AEAlk) ! 3 times higher than those dividing exponentially (1.5-2 pg cell À1 ), and the U 37 K 0 of ''excess'' alkenone dropped by 0.11 units. In contrast, 5 days of continuous darkness resulted in a 75% decrease in cellular AEAlk and a significant U 37 K 0 increase (+0.11 units). Given an established 0.034 unit/°C response for exponentially growing cells of this strain, the observed range of U 37 K 0 variability at 15°C corresponds to an uncertainty of ±3.2°C in predicted growth temperature. This level of variability matches that of the global U 37 K 0 annual mean sea surface temperature calibration for surface marine sediments, begging the question: What is the physiological condition of alkenone-producing cells exported to marine sediments? Comparison of our laboratory results for a strain of E. huxleyi isolated from the subarctic Pacific Ocean with depth profiles for alkenones in surface waters from two contrasting sites in the northeast Pacific Ocean suggests that the answer to this question depends on the ocean regime considered, a possibility with significant bearing on how stratigraphic U 37 K 0 records in marine sediments are to be interpreted paleoceanographically.

Storage lipids of fifth copepodites (C5) of Culanus$nmarchicus from Georges Bank and the Gulf of Maine were quantified from video images and by Iatroscan (thin-layer chromatography with flame-ionization detection, FID). Oil withdrawn from the oil sac by micropipette was pure wax ester (WE); triacylglycerols (TAG) were elsewhere in the body. Video images indicated more WE than could be demonstrated by Iatroscan. This was due to greater FID response to pure, commercially available waxes with low levels of unsaturation than to mixtures of mostly polyunsaturated wax in C. jinmarchicus. A revised calibration scheme uses both WE and TAG purified in bulk by silica gel chromatography from C. finmarchicus itself. Use of quadratic calibration curves allowed analysis of single specimens, showing the individual variability of lipid class composition. C5 collected in April-July, while presumably storing lipid for the resting stage, showed a nearly constant level of TAG, -17 pg ind.-I, whereas WE amounts varied from nearly 0 to >300 /lg ind.-'. There appears to be a TAG quota that is filled before WE accumulates significantly and that is usually not exceeded. Many C5 collected in February and March had very high amounts and fractions of TAG. This likely results from transformation of stored WE to TAG in preparation for egg production.

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