Updated at 6.28pm: The amount of construction waste disposed of at public landfills has decreased 40 per cent over the last four years, Secretary for the Environment, Transport and Works Sarah Liao Sau-tung said on Friday. Dr Liao was speaking at ?Green Construction ? We Must Do Better?, organised by the Hong Kong Construction Association at the Hong Kong Convention and Exhibition Centre on Friday. She said that there were eight million tonnes of construction and demolition (C&D) materials dumped at public landfills last year, a drop of about 40 per cent from about 13 million tonnes in 2002. ?Another achievement is the remarkable increase in the amount of C&D materials reused,? she added. The secretary explained that in the past four years the amount of surplus rock, which had been processed and re-used as aggregates increased from just 0.04 million tonnes in 2002 to over three million tonnes last year. In January the government introduced charges on construction waste in order to ease pressure on landfills. Under the policy, it costs $125 per tonne to dump construction waste in landfills, compared with $100 per tonne for partially sorted waste and $27 for fully sorted waste. Dr Liao stressed the importance of the ?daunting task? to tackle the large amount of construction waste produced in Hong Kong. She also called on green design approaches to be given a higher priority in both private and public projects from the early design stage. ?I am aware that this cannot be achieved without the full support of the management of the private sector and public corporations,? she said, ?therefore I appeal for positive response and action to promote green designs in all your projects.?