Purpose About 143,000 industrial chemicals have been pre-registered at the European Chemical Agency for registration according to REACH. The tools, models, and regressions employed for the chemical safety assessment of the registered compounds have limited applicability domains. Thus, it is an important question which fraction of the pre-registered compounds falls into these applicability domains. Methods A random sample of 1,510 compounds out of the ∼117,000 chemicals pre-registered at the European Chemicals Agency and due to registration by 2010 and 2013 was analyzed to investigate the physico-chemical domain of REACH substances. The chemical structure was identified from the CAS number, and the software ACD/Labs was used to calculate dissociation constant(s) (pK a ), octanolwater partition coefficient (log P) and vapor pressure of the neutral molecule. Results Four hundred ninety-one (33%) of the 1,510 compounds are mostly ionized at pH7 (i.e., acids pK a <7, bases pK a >7). Twenty-seven percent of compounds are acids with pK a <12, 14% bases with pK a >2, and 8% ampholytes or zwitterionics. Almost half of the ionizable compounds (267 out of 1,510 compounds or 18%) with pK a between 2 and 12 are even multivalent. There is a high occurrence of hydrophilic chemicals (30% with log P<1), but super-lipophilic chemicals are frequent as well (10% with log P>6). Most chemicals are non-or semi-volatile: the vapor pressure is <1 Pa for 65% and >100 Pa only for 13%. Conclusions This preliminary characterization of the REACH chemical space helps to identify most urgent gaps of existing in silico tools that are going to be applied in the context of REACH. These data may also be used to select representative sets of test chemicals for the development of new QSARs and models.
Keywords:Integrated water resources management (IWRM) Hydroeconomic modeling Stochastic dynamic programming (SDP) Water quality management Water value River basin s u m m a r y A hydroeconomic optimization approach is used to guide water management in a Chinese river basin with the objectives of meeting water quantity and water quality constraints, in line with the China 2011 No. 1 Policy Document and 2015 Ten-point Water Plan. The proposed modeling framework couples water quantity and water quality management and minimizes the total costs over a planning period assuming stochastic future runoff. The outcome includes cost-optimal reservoir releases, groundwater pumping, water allocation, wastewater treatments and water curtailments. The optimization model uses a variant of stochastic dynamic programming known as the water value method. Nonlinearity arising from the water quality constraints is handled with an effective hybrid method combining genetic algorithms and linear programming. Untreated pollutant loads are represented by biochemical oxygen demand (BOD), and the resulting minimum dissolved oxygen (DO) concentration is computed with the Streeter-Phelps equation and constrained to match Chinese water quality targets. The baseline water scarcity and operational costs are estimated to 15.6 billion CNY/year. Compliance to water quality grade III causes a relatively low increase to 16.4 billion CNY/year. Dilution plays an important role and increases the share of surface water allocations to users situated furthest downstream in the system. The modeling framework generates decision rules that result in the economically efficient strategy for complying with both water quantity and water quality constraints.
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