Elimination is rapid at first (half-life of 1–2 days), by methylation to monomethylarsonic acid and dimethylarsinic acid, and excretion in the urine, but a certain amount (30–40% in the case of repeated exposure) is incorporated into the bones, the muscles, the skin, the hair and 
the nails (all tissues rich in keratin) and eliminated over a period of weeks or months. The first symptoms of acute arsenic poisoning by ingestion are digestive problems: vomiting, abdominal pains, diarrhea often accompanied by bleeding. Sub-lethal doses can lead to convulsions, cardiovascular problems, inflammation of the liver and kidneys and abnormalities in the coagulation of the blood. These are followed by the appearance of characteristic white lines (Mees lines) on the nails and by hair loss. Lower doses lead to liver and kidney problems and to changes in the pigmentation of the skin. Even dilute solutions of arsenic trioxide are dangerous on contact with the eyes. The poisonous properties are well known and the subject of an extensive literature.Chronic arsenic poisoning is known as arsenicosis. This disorder affects workers in smelters, in populations whose drinking water contains high levels of arsenic (0.3–0.4 ppm), and in patients treated for long periods with arsenic-based pharmaceuticals. Similarly, studies on workers exposed in copper foundries in the U.S., Japan and Sweden indicate a risk of lung cancer 6–10 times higher for the most exposed workers compared with the general population. Long-term ingestion of arsenic trioxide either in drinking water or as a medical treatment can lead to skin cancer.
Differential diagnosis
Neck pain may come from any of the structures in the neck including: vascular, nerve, airway, digestive, and musculature / skeletal, or be referred from other areas of the body.Major and severe causes of neck pain (roughly in order of severity) include:

Carotid artery dissection
Referred pain from acute coronary syndrome
Head and neck cancer
Infections, including:
Meningitis of several types including sudden onset of severe neck or back pain particularly in teens and young adults which may be fatal if not treated quickly
Retropharyngeal abscess
Epiglottitis
Spinal disc herniation – protruding or bulging discs, or if severe prolapse. Spondylosis - degenerative arthritis and osteophytes
Spinal stenosis – a narrowing of the spinal canalMore common and lesser neck pain causes include:

Stress – physical and emotional stresses
Prolonged postures – many people fall asleep on sofas and chairs and wake up with sore necks. Minor injuries and falls – car accidents, sporting events, and day to day injuries that are really minor. Referred pain – mostly from upper back problems
Over-use – muscular strain is one of the most common causes
Whiplash
Pinched nerveAlthough the causes are numerous, most are easily rectified by either professional help or using self help advice and techniques. More causes can include: poor sleeping posture, torticollis, head injury, rheumatoid arthritis,
Carotidynia, congenital cervical rib, mononucleosis, rubella, certain cancers, ankylosing spondylitis,
cervical spine fracture, esophageal trauma, subarachnoid hemorrhage, lymphadenitis, thyroid trauma, and tracheal trauma. Treatment
Treatment of neck pain depends on the cause. For the vast majority of people, neck pain can be treated conservatively. Recommendations in which it helps alleviate symptoms include applying heat or cold.