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This paper presents emission factors (EFs) derived for a range of persistent organic pollutants (POPs) when coal and wood were subject to controlled burning experiments, designed to simulate domestic burning for space heating. A wide range of POPs were emitted, with emissions from coal being higher than those from wood. Highest EFs were obtained for particulate matter, PM10, (approximately 10 g/kg fuel) and polycyclic aromatic hydrocarbons (approximately 100 mg/ kg fuel for sigmaPAHs). For chlorinated compounds, EFs were highest for polychlorinated biphenyls (PCBs), with polychlorinated naphthalenes (PCNs), dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) being less abundant. EFs were on the order of 1000 ng/kg fuel for sigmaPCBs, 100s ng/ kg fuel for sigmaPCNs and 100 ng/kg fuel for sigmaPCDD/Fs. The study confirmed that mono- to trichlorinated dibenzofurans, Cl1,2,3DFs, were strong indicators of low temperature combustion processes, such as the domestic burning of coal and wood. It is concluded that numerous PCB and PCN congeners are routinely formed during the combustion of solid fuels. However, their combined emissions from the domestic burning of coal and wood would contribute only a few percent to annual U.K. emission estimates. Emissions of PAHs and PM10 were major contributors to U.K. national emission inventories. Major emissions were found from the domestic burning for Cl1,2,3DFs, while the contribution of PCDD/F-sigmaTEQ to total U.K. emissions was minor.

Synovial fluid lubricates joints and tendon sheaths, and carries metabolites to and from the avascular articular cartilage. The fluid is generated primarily by ultrafiltration of synovial microvascular plasma into the joint cavity when intra-articular pressure is low, as in extension. Hyaluronan is added to the fluid by actively secreting synoviocytes in the lining. The role of hyaluronan as a hydrodynamic lubricant has long been recognized. A second hydraulic role was suggested recently, namely the conservation of intraarticular fluid during joint flexion. This idea arose from the observation that, as intra-articular pressure is raised, the opposition to fluid drainage from the joint cavity increases if hyaluronan is present, but not when it is absent (McDonald & Levick, 1995). The present study explores new facets of this action and its mechanism. Hyaluronan is a non-sulphated glycosaminoglycan chain of variable length. Native chains in synovial fluid have a molecular mass of (2-7) ² 10É Da. In some commercial preparations, however, the molecular mass can be an order of magnitude smaller, and this was the case with the umbilical cord hyaluronan studied previously (McDonald & Levick, 1995). Despite this, umbilical hyaluronan greatly reduces the trans-synovial escape of fluid from the joint cavity in rabbit knees, and alters the fundamental shape of the pressure-flow relation. In the absence of hyaluronan, the relation between intra-articular pressure and trans-

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