**4. Discussion**

This paper interpreted the evolution of health risks associated with rapid urban expansion from a spatiotemporal perspective based on the case of Changzhou, China. The results showed that the pattern of Changzhou's urbanization is a typical case of industrial land expansion, which aggravated environmental pollution. Health risks in Changzhou tended to increase over time and with proximity to pollution. This kind of urbanization exposed the population to a polluted environment, and was related to increased health risks and the frequent occurrence of environmental health events.

With rapid urbanization, urban residents face decreasing environmental benefits, and even suffer a poisoned environment when pollutant emissions proliferate in the urban space. Furthermore, the development of industry increases pollution sources and extends the spatial distribution of pollutants, especially with people living close to past or current industrial sites [29,41–43]. In general, industrial urbanization exposes an increasing number of people to a polluted environment, and long-term pollution exposure is related to increased health risks. The spatiotemporal perspective here adopted can help facilitate an understanding of the mechanism and spatiotemporal patterns of health risks, and risk assessments of environmental health.

High-resolution spatiotemporal data can mitigate uncertainties and bias in exposure assessments [44,45]. However, there are few monitoring platforms and databases for gathering spatiotemporal data on chronic non-communicable diseases and human mortality in China. The spatiotemporal discontinuity of environmental health events and privacy issues related to diseases caused by pollution present challenges for quantitative analyses of the relationship between land-use change and health. In our study, however, we collected multi-source data in an effort to explain this relationship. Our results showed that Changzhou's urbanization featured rapid development, rapid population growth, extensive urban land expansion, and industrialization dominated by heavy industry (Figure 2). Industrial waste emissions increased alongside increasing population levels in a worsening environment (Figure 3). Further, increases in the total death rate of the city's population, the number of cancer cases, and cancer mortality support the pattern of exacerbated health risks (Figure 4).

Increases in new construction land and high-polluting enterprises showed clusters of High–High in the inner suburban areas of Changzhou, an exurb area of Changzhou, and a suburban area in Jintan district, indicating that urban expansion presented a high spatial association with variations in enterprises of high-polluting industries (Figure 5e,f). The spatial distribution of environmental health events presented spatial adjacency with enterprises of high-polluting industries or brownfields (Figure 6). This indicated that urbanization exposed people to polluted environments and caused environmental health events. In particular, cancer events in Xinbei and Wujin were both adjacent to highpolluting enterprises.

The results of the GAM analysis also revealed that rapid urban land expansion resulted in increased health risks. The total mortality and the number of cancer cases generally increased along with the development of urbanization factors, including population, land use, and industry. The variation in total mortality showed a nonlinear response to the construction land area, and even transformed when the construction land area reached 200 km2 (Figure 7(a2)). Larger construction land or urban space may disperse concentrated populations to avoid gathering around pollution sources, and restrain increases in environmental health risks. Increases in the urbanization rate and construction land area were also found to be related to increases in cancer mortality. According to the data on health risks, these increased along with the development of urbanization.

There were differences in the time ranges for several kinds of data. Changzhou's administrative division has changed since 2002. Thus, we selected the period from 2003–2018 when calculating the urbanization rate. The total population and industrial waste emissions are measured for the entire city, and thus cannot be divided into administrative division. Therefore, we selected a longer time range. There were no long-term data on cancer because monitoring platforms on chronic non-communicable diseases were only recently introduced in China. Thus, we extrapolated relevant health data and events from literature and media coverage. When we conducted statistical analyses, mainly in the GAM model, the common time range was used to treat the discrepancies.

Our results have some policy implications. First, more attention should be paid to environmental health. The government should inspect, analyze, and transform current urbanization patterns with rapid industrial land expansion. Urbanization plans should consider the increase in population, industrial development, and urban expansion, and environmental assessments are needed for redevelopment plans and new extensions of land. Second, monitoring databases and platforms for land pollution and public health are urgently needed and should be accessible to the public. Complete real-time data can help interpret the dynamics of pollution and health and assist with risk warning. Besides, environmental impact assessment should be paid sufficient attention to support urban functional zoning in future. Strict and scientific criteria related to environmental health should be set and strictly enforced, including safe distances between urban land space and industrial sites or brownfield land, and safe pollutant emission standards. Precaution is more important than governance.
