1. Introduction
Agricultural land is the material basis and source of wealth for human
survival and development, as well as an important site for the
migration, transformation, and deposition of heavy metals. Over the past
decades, China’s rapid urbanization and industrialization have generated
significant emissions of heavy metal pollutants, and the accumulated
heavy metals are transformed into organic complexes through organisms in
the soil, which are persistent, non-degradable and bioaccumulative,
posing a serious threat to the health of urban and rural habitats and
the ecological and environmental security of agricultural land.(Dai et
al., 2018; Zang et al., 2017) It poses a serious threat to the
environmental health of urban and rural people and the ecological safety
of agricultural land. Due to the rigidity of the demand for food and
agricultural products caused by the huge population in China,
agricultural production has to rely on intensive farming and high rates
of fertilizer and pesticide application to ensure yield, thus causing a
decline in the quality of agricultural land and a further increase of
risk of heavy metal contamination in the soil.(Shang, Xu, Zhang, &
Huang, 2018; G. Wang et al., 2017) About 10% of China’s arable soils
are contaminated with heavy metals to varying degrees, according to
research findings, and the exceedance rate of heavy metals in arable
soils in the main grain-producing regions of China is 21.49%, which is
highly concentrated in urban areas, especially in the peripheral urban
agricultural areas where pollution is relatively low.(Chabukdhara &
Nema, 2013; Shang et al., 2018; Q. Yang et al., 2018) The rate of
exceedance was 21.49% and was highly concentrated in urban areas,
especially in agricultural areas in the periphery of cities with
relatively low pollution.
While arable soil in the urban periphery play an important role in
providing a daily supply of agricultural products for residents and in
the health of urban and rural ecosystems, the level of heavy metal
contamination in arable soil is directly related to food safety and the
well-being of agroecosystems.(Fujita et al., 2014; Lu & Yu, 2018)
Therefore, the potential heavy metal contamination in peri-urban
agricultural land has become an important challenge in the rapid
urbanization process in China, and its changes in content, sources, and
spatial and temporal distribution patterns should be of great concern.
At present, studies on heavy metals in arable soil mainly focus on
content characteristics, spatial distribution, pollution level, source
analysis, and health risks.(Dong et al., 2019; Ismail Umer, Younis
Fatah, Ramadhan Abdo, Abdulaziz Karim, & Nabil Abdulrahman, 2021;
Mapani et al., 2010) The spatial pattern of soil heavy metals is largely
caused by present and past human activities, such as industrial
agriculture, due to their significant cumulative nature.(Y. Wang, Duan,
& Wang, 2020) . Therefore, the application of multi-period heavy metal
content measurement, spatial and temporal variation analysis of
pollution, and pollution source analysis can more accurately reveal
sources and spatial and temporal distribution patterns of heavy metal
pollution in soils, and can effectively curb the deteriorating trend of
soil pollution(H. Y. Chen, Teng, Wang, Song, & Zuo, 2013) It can
effectively curb the deterioration of soil pollution. The study of
spatial and temporal variability of soil heavy metal pollution can be
carried out by comparing spatial interpolation maps of different periods
based on geostatistical methods through GIS characterization.(X. Li et
al., 2012; Y. Yang, Wu, & Christakos, 2015) Heavy metal spatial
variability can be studied by GIS characterization and geostatistical
method comparing spatial interpolation maps in different periods. Soil
heavy metal pollution source analysis methods include the Emission
inventory method, Chemical massbalance (CMB) in receptor model, Hybrid
approach, Positive Matrix Factorization (PMF), UN-MIX model, etc.(Lang,
Li, Wang, & Peng, 2015; Y. Liu, Liu, Yousaf, Zhang, & Zhou, 2020; Wu,
Li, Teng, Chen, & Wang, 2020) Among them, PMF was first used for source
of atmospheric airborne particulate matter analysis in the 1990s, and in
recent years it has also been widely used for soil analysis.(Tan et al.,
2016) It is a new and effective method for source analysis of heavy
metals, which is easy to operate and effective in identifying the
sources and assigning their contribution to each heavy metal.(Chai et
al., 2021) It is a simple and effective method to analyze source heavy
metals.
Chengdu is a central city in
western
China and a typical representative of the fast-growing cities in China
in recent years. At the same time, as an important food and agriculture
production base in China, it also carries the important responsibility
of food security in China. However, there are still ecological risks of
soil heavy metals in this region. Numerous scholars have conducted
studies to assess the pollution of cultivated soils in Chengdu.(Pang,
Li, Zhang, Wang, & Yu, 2011; S, H, Q, Y, & H, 2013) .However, current
studies on soil contamination in the region are mainly limited to
specific administrative regions, specific periods, or specific soil use
types, while there are relatively few systematic studies on the levels,
sources, spatial and temporal patterns of hazardous metals on
agricultural land in different urban circles in the context of rapid
urbanization. The Chinese government has proposed a strategy to build
the Chengdu-Chongqing City Cluster to guide the growth of west China and
to boost the integration and interplay with the ‘Belt and Road’ and
Yangtze River Economic Belt construction strategies. The research can
give useful direction to the development of relevant policies. In
addition, the study of heavy metal contamination in arable soils in
Chengdu will not only improve the understanding of arable soils in the
Yangtze River upstream area, but also provide a basis for arable soil
conservation and management in the rapidly urbanizing areas of China.
The primary goals from the study were to (1) analyze the spatial and
temporal patterns of soil heavy metal contamination in farmlands of
typical rapidly developing cities in China; and (2) analyze causes and
effects between soil pollution sources and soil pollution and
environmental variables in agricultural fields of different circles of
rapidly developing cities. We hypothesize that ”rapid urban development
and human activities are the key drivers of increasing soil heavy metal
pollution over time and space” in the study area. Management decisions
require a process-based analysis of pollution sources and capture key
factors in terms of their spatial and temporal dimensions.