Metal leaching from the bridge paint waste in the presence of steel grit

A review of blasting waste generation and management in the ship repair industry

Solid blasting waste generated from coating removal during ship repair and maintenance poses environmental challenges. This paper presents a review of the generation, characterization, and treatment of blasting waste in the ship repair industry. The quantities, properties, and environmental impacts of the generated blasting waste are summarized and analyzed, and the results indicate that blasting waste has a high generation rate and/or high toxicity. As alternatives to landfill, available blasting waste treatment methods include hydrometallurgical leaching, physical/physicochemical separation, thermal treatment, and direct utilization in the production of building materials. The advantages and disadvantages of these treatments are reviewed and compared. The production of building materials from blasting waste is currently attractive owning to its economic benefits and technical simplicity, whereas recycling blasting waste for high-value applications is gradually gaining research interest. The high dependence of the choice and performance of treatment methods on the waste type and characteristics is highlighted. The results emphasize the interest in conducting more research on physiochemical and thermal properties and the environmental effects of blasting waste. This review suggests that future research should focus more on paint waste management because of the restricted application of dry abrasive blasting and the development of nonabrasive blasting methods in the ship repair industry.

Paint particles in the marine environment: An overlooked component of microplastics

Because paint particles consist of a resin (polymer) combined with one or more additives, they bear compositional similarities with microplastics. Despite these shared characteristics, however, paint particles are often undetected, deliberately overlooked or evade classification in the pool of micro-debris (all synthetic debris of < 5 mm in size), and in particular in the marine setting where an extensive body of microplastic literature exists. Accordingly, the present paper provides a critical insight into the physico-chemical properties, sources, distributions, behaviour and toxicity of paint particles in the marine environment. Paint particles contain a greater proportion of additives than plastics and, consequently, are more brittle, angular, opaque, dense, heterogeneous and layered than microplastics of equivalent dimensions. Land-based sources of paint particles, including deteriorating or disturbed coatings on roads and building, are transported to the ocean with other microplastics via urban runoff, water treatment facilities and the atmosphere. However, inputs of paint particles are enhanced significantly and more directly by the disturbance, erosion and weathering of coatings on coastal structures, boats and ships. Estimates of paint particle emissions to the marine environment vary widely, with calculated contributions to the total synthetic micro-debris input as high as 35%. Upper estimates are consistent with available (albeit limited) quantitative information on the relative abundance of paint particles amongst synthetic material captured by sea surface trawls and ingested by marine animals. Of greatest environmental concern is the high chemical toxicity of paint particles compared with similarly-sized microplastics and other synthetic debris. This results from the contemporary and historical use of high concentrations of hazardous inorganic additives in marine antifouling and land-based paints, and the relatively ready mobilisation of harmful ions, like Cu⁺/Cu²⁺, TBT⁺, Pb²⁺ and CrO₄ ^2-, from the matrix. Recommendations arising from this review include greater use of particulate capturing devices, waste collection systems and recycling facilities during paint disturbance, raising awareness of the potential impacts of discarded paint amongst users, and alerting the microplastic community to the significance of paint particles and developing means by which they are isolated from environmental samples.

Lead in plastics - Recycling of legacy material and appropriateness of current regulations

X-ray fluorescence spectrometry has been employed to measure Pb in a wide range of consumer and environmental plastics, including food-packaging material, household goods, electronic casings, beach litter and agricultural waste. Results reveal high concentrations of Pb (>1000 mg kg^-1) in historical items that are still in use or circulation (e.g. toys, construction plastics, wiring insulation) and variable, but generally lower concentrations in more recently manufactured articles. Analysis of Br, Cl and Cr, proxies for brominated flame retardants, polyvinyl chloride (PVC) and chromate pigments, respectively, suggests that as historical material is recycled, Pb from electronic plastics and pigments, but not PVC, is dispersed into a variety of newer products. Although most cases in the consumer sector comply with relevant EU Directives, some products that are non-compliant highlight shortfalls in regulations where recycling is involved and potential problems arising from the direct fashioning of industrial plastics into new consumer goods through attempts to be environmentally positive. The uncontrolled loss of historical and recycled plastics has also resulted in Pb contamination of the environment. Here, it is proposed that litter can be classified as hazardous depending on its Pb content and according to existing regulations that embrace consumer plastics.

Field methods for rapidly characterizing paint waste during bridge rehabilitation

For Department of Transportation (DOT) agencies, bridge rehabilitation involving paint removal results in waste that is often managed as hazardous. Hence, an approach that provides field characterization of the waste classification would be beneficial. In this study, an analysis of variables critical to the leaching process was conducted to develop a predictive tool for waste classification. This approach first involved identifying mechanistic processes that control leaching. Because steel grit is used to remove paint, elevated iron concentrations remain in the paint waste. As such, iron oxide coatings provide an important surface for metal adsorption. The diffuse layer model was invoked (logKMe=4.65 for Pb and logKMe=2.11 for Cr), where 90% of the data were captured within the 95% confidence level. Based on an understanding of mechanistic processes along with principal component analysis (PCA) of data obtained from field-portable X-ray fluorescence (FP-XRF), statistically-based models for leaching from paint waste were developed. Modeling resulted in 96% of the data falling within the 95% confidence level for Pb (R(2) 0.6-0.9, p ⩽ 0.04), Ba (R(2) 0.5-0.7, p ⩽ 0.1), and Zn (R(2) 0.6-0.7, p ⩽ 0.08). However, the regression model obtained for Cr leaching was not significant (R(2) 0.3-0.5, p ⩽ 0.75). The results of this work may assist DOT agencies with applying a predictive tool in the field that addresses the mobility of trace metals as well as disposal and management of paint waste during bridge rehabilitation.

Metal concentrations and distribution in paint waste generated during bridge rehabilitation in New York State

Between 1950 and 1980, lead and chromium along with other metals have been used in paint coatings to protect bridges from corrosion. In New York State with 4500 bridges in 11 Regions 2385 of the bridges have been rehabilitated and subsequently repainted after 1989 when commercial use of lead based paint was prohibited. The purpose of this research was to address the concentration and distribution of trace metals in the paint waste generated during bridge rehabilitation. Using hypothesis testing and stratified sampling theory, a representative sample size of 24 bridges from across the state was selected that resulted in 117 paint waste samples. Field portable X-ray fluorescence (FP-XRF) analysis revealed metal concentrations ranged from 5 to 168,090 mg kg(-1) for Pb, 49,367 to 799,210 mg kg(-1) for Fe, and 27 to 425,510 mg kg(-1) for Zn. Eighty percent of the samples exhibited lead concentrations greater than 5000 mg kg(-1). The elevated iron concentrations may be attributed to the application of steel grit as an abrasive blasting material routinely used by state Departments of Transportation in the paint removal process. Other metals including Ba and Cr were observed in the paint waste as well. As a result of the paint formulation, metals were found to be associated in the paint waste (Pb correlated with Cr (r=0.85)). The elevated metal concentrations observed raises concern over the potential impact of leaching from this waste stream.