Plantand Soil 171: 303-316, 1995. © 1995 KluwerAcademicPublishers. Printed in the Netherlands. Effect of wastewater sludge on growth and heavy metal bioaccumulation of two Salix species Michel Labrecque, Traian I. Teodorescu and St6phane Daigle lnstitut de Recherche en Biologie Wgdtale, Jardin Botanique de Montrdal, 4101 Sherbrooke Est, Montrdal, Qudbec, Canada, HIX 2B2 Received2 May 1994.Accepted in revisedform3 October1994 Key words: bioavailability, fertilization, heavy metals, productivity, Salix, wastewater sludge Abstract Fast-growing tree species, such as willows, can benefit from sludge application. While sludges are good fertilizers, they may contain heavy metals which could reduce productivity and cause environment risks. The aims of the present research were to: i) determine the biomass production of Salix discolor Mtihl. and Salix viminalis L. when supplied with various amounts of dried and pelleted sludge and ii) assess the uptake and accumulation of heavy metals. Trials were carried out using unrooted cuttings that were planted in large plastic pots containing sandy soil and grown outdoors for a 20-week period. Five doses of sludge were applied: the equivalents of 0 (TO), 40 (T1), 80 (T2), 120 (T3), 160 (T4) and 200 (T5) kg "available" N ha -l . Trees which received the highest dosage of sludge showed the best growth. Stem biomass was significantly greater for S. viminalis which had received sludge treatments. The relationship between the total biomass yield Y (g) and the rate of fertilization X (equivalent to kg of "available" nitrogen provided per hectare) is linear. Regression equations of predicted biomass production were established as follows: S. discolor, Y = 28.36 + 0.56X and S. viminalis, Y = 39.95 + 0.64X. For both species, the greatest stem biomass per g of N applied was produced with treatments 4 and 5. Amounts of nitrogen per leaf area (N/LA) and per dry leaf mass (N/DL) were higher for S. viminalis. The metal transfer coefficient did not vary between the species but was significantly different for Cd and Zn. Plants were able to absorb Cd and Zn, but were less able to absorb Ni, Hg, Cu, and Pb. It was concluded that the dried and pelleted sludge is a good fertilizer. S. discolor and particularly S. viminalis can be used as filters for the purification of wastewater sludge as well as for biomass production purposes. Introduction Wastewater sludges produced by sewage treatment plants are a good source of macroelements and microelements and generally contain a high quantity of organic matter. Their application in agriculture and in silviculture translates into improved soil fertility. Sludges also help maintain soil structure, soil water- holding ability, soil cation exchange capacity, and soil biological activity (Giroux and Tabi, 1990). Although the recycling of sludge is an attractive alternative, its use often brings about certain risks to the environment caused by accumulation of heavy met- als and organic compounds and potential contamina- tion from pathogenic organisms. In Quebec (Canada), standards have been set to establish acceptable levels of these contaminants in the sludge and in fertilized soils (MENVIQ, MAPAQ, 1991). The standards take into account only the total quantity of metals in the soil. In order to increase accuracy and reduce envi- ronmental risks, an evaluation of the bioavailability of metals to the plants and the heavy metal content in soil solutions and ground water is necessary. For this evaluation, assessment of the degree of solubility of metals in the water is important (Petruzzelli et al., 1985; Petruzzelli, 1989). High metal content in agricultural crops is not desir- able and is potentially dangerous. For trees, a higher metal content is acceptable as long as normal phys- iological activity is not affected. Generally, natural