A new in situ magnetic method to indicate the source and seasonal diffusion of heavy metal contamination at Qingdao Beach, China

The accumulation of heavy metals from sewage and garbage dumping can seriously impact beach tourism and thus the local economy, but it is difficult to quickly and accurately determine the pollution location and source of heavy metals and clarify their diffusion range. This study investigates a new in situ magnetic testing method to address this issue. (1) The in situ method can be used to effectively and quickly evaluate heavy metal sources and diffusion ranges based on the distribution of κ values. (2) According to chemical experiments, the specific elements polluting a beach can be determined, such as the Cr, Ni, Zn, and Fe pollution of Beach No. 3. (3) Although κ values for assessing heavy metal pollution on different beaches vary, metal pollution occurs when the higher κ value is more than 50 times the lower κ value on the same beach. (4) The κ values vary in different seasons due to the influence of natural factors and urban seasonal sewage policies. •In situ magnetic method is effective to evaluate heavy metal pollution on beaches.•The critical magnetic values of 600, 1500 and 3000 SI indicate slight to heavy pollution.•Pollution may occur when the magnetic values are more than 50 times the lower values.•Cr, Fe, Ni and Zn pollutants were sourced from sewage and dumped burning cinder.•Polluted beach in summer and winter has higher values due to tourist and sewage policies.