This week, the overall grades of four chemicals stocks are lower, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Tronox Ltd. (TROX) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Tronox produces and markets titanium dioxide. The stock also earns F’s in Portfolio Grader’s specific subcategories of Earnings Momentum, Earnings Revisions, Equity and Margin Growth. For more information, get Portfolio Grader’s complete analysis of TROX stock.

Calgon Carbon Corporation (CCC) earns a D this week, moving down from last week’s grade of C. Calgon Carbon is engaged in products and services for purifying water and air. To get an in-depth look at CCC, get Portfolio Grader’s complete analysis of CCC stock.

Marrone Bio Innovations, Inc. (MBII) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). The stock receives F’s in Earnings Momentum, Equity, Cash Flow and Sales Growth. For more information, get Portfolio Grader’s complete analysis of MBII stock.

The rating of Rockwood Holdings, Inc. (ROC) declines this week from a C to a D. Rockwood Holdings is a global developer, manufacturer and marketer of value-added specialty chemicals and advanced materials used for industrial and commercial purposes. The stock gets F’s in Earnings Growth, Earnings Surprise and Margin Growth. To get an in-depth look at ROC, get Portfolio Grader’s complete analysis of ROC stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.