## 1 Introduction  
Soil is an extremely valuable natural resource and a crucial supply for agricultural production and human survival. With the rapid development of today's society, along with accelerated industrialization and urbanization, the quality of the soil environment is progressively deteriorating. Among these concerns, heavy metal pollution in soil stands out as one of the most severe issues related to soil contamination [1, 2]. Heavy metals are persistent, latent, cumulative, biotoxic and irreversible, and their accumulation in arable soils changes the physical and chemical properties of the soil, affects the microbial community in the soil, thereby interfering with the self-purification and fertility of the soil and destroying the soil structure and ecosystem [3, 4]. These changes can lead to a reduction in crop yield and quality, such as Cd, Pb affect photosynthesis and nutrient uptake in plants, affecting the nutritional value of the crop; Zn is an essential element for plant growth, but is toxic to plants when Zn concentrations are too high [5]. The accumulation of heavy metals in soil can lead to the accumulation of heavy metals in crops and enter the human body through the food chain, posing a threat to human health. For example, the accumulation of Cu can cause hypotension, jaundice, Menke's disease, and so on [6]; the accumulation of As and Hg can induce a variety of cancers and Blackfoot disease [7]; the accumulation of Pb can affect human intelligence and bone development, damage renal function and immune function [8]; excessive Cr can cause respiratory diseases, causing emphysema and other diseases [9]; the accumulation of Cd can cause bone pain, and also pose a serious threat to human liver and kidney function [10]. At the same time, heavy metals in soil can pollute surface water and groundwater with surface runoff, rainfall infiltration, etc., and can also enter the atmosphere by wind, affecting the quality of the ecological environment. A multitude of studies have demonstrated that the migration, transformation, and toxicological impacts of heavy metals in soil are not solely dependent on their total quantity, but also intricately linked to their occurrence form and concentration. The analysis of heavy metal speciation forms in soil is particularly crucial for assessing soil heavy metal pollution [11; 12; 13]. Therefore, the improved BCR sequential extraction procedure with higher accuracy and stability was adopted in this study to analyze the content of various forms of heavy metals in soil in the study area and explore the distribution characteristics of their occurrence forms [11]. The Zhaoping County in Hezhou, Guangxi is abundant in mineral resources, with its gold reserves and exploitation playing a significant role in the southeastern region of Guangxi, which is recognized as a pivotal area for gold mining [14]. The former Jinzhuzhou gold mine in Pingshui Village, where the research area is located, has been subjected to unregulated mining practices for an extended period since its discovery. Consequently, the resulting waste gas, wastewater, and solid waste were discharged and discarded without proper treatment. This irresponsible behavior has led to severe pollution of the mine environment, downstream Pingshui flushing water quality, and cultivated land on both sides of the river. Moreover, it has had a detrimental impact on local production and livelihoods. The Pingshui flushing has a total length of approximately 8 km, with around nine tributaries. Wastewater generated from the mine flows out from the source of Pingshui flushing and merges with the Southwest Rusch to flow into the Gui River, and the historical data show that the water quality of the mainstream of Pingshui flushing is relatively stable. However, the tributary streams frequently have exceeding levels of pH or As, and the water quality of the upstream tributaries of Pingshui flushing which flows through the mine is unstable.